Fixes and improvements to the README (#748)

* Fix rootValue option description

The mentioned function should be execute() instead of graphql(). Also,
the branch name and line number have changed.

* Fix context option description

The mentioned function should be execute() instead of graphql() and the
passed property should be contextValue instead of context. Also, the
branch name and line number have changed.

* Remove distracting session middleware from extensions example

Using the session middleware in the extensions example seems unnecessary
and distracting from the extensions example.

* Make list items explaining POST body parsing consistent

* Add missing comma in JSON example

* Improve the readability of some sentences

* Fix some small typos

* Add missing backticks

* Fix branch name in links to graphql-js repo

Author: kyarik

README.md

@@ -131,18 +131,18 @@ The `graphqlHTTP` function accepts the following options:
 
   - **`defaultQuery`**: An optional GraphQL string to use when no query
     is provided and no stored query exists from a previous session.
-    If undefined is provided, GraphiQL will use its own default query.
+    If `undefined` is provided, GraphiQL will use its own default query.
 
-  - **`headerEditorEnabled`**: An optional boolean which enables the header editor when true.
-    Defaults to false.
+  - **`headerEditorEnabled`**: An optional boolean which enables the header editor when `true`.
+    Defaults to `false`.
 
   - **`subscriptionEndpoint`**: An optional GraphQL string contains the WebSocket server url for subscription.
 
-- **`rootValue`**: A value to pass as the `rootValue` to the `graphql()`
-  function from [`GraphQL.js/src/execute.js`](https://github.com/graphql/graphql-js/blob/master/src/execution/execute.js#L119).
+- **`rootValue`**: A value to pass as the `rootValue` to the `execute()`
+  function from [`GraphQL.js/src/execute.js`](https://github.com/graphql/graphql-js/blob/main/src/execution/execute.js#L129).
 
-- **`context`**: A value to pass as the `context` to the `graphql()`
-  function from [`GraphQL.js/src/execute.js`](https://github.com/graphql/graphql-js/blob/master/src/execution/execute.js#L120). If `context` is not provided, the
+- **`context`**: A value to pass as the `contextValue` to the `execute()`
+  function from [`GraphQL.js/src/execute.js`](https://github.com/graphql/graphql-js/blob/main/src/execution/execute.js#L130). If `context` is not provided, the
   `request` object is passed as the context.
 
 - **`pretty`**: If `true`, any JSON response will be pretty-printed.
@@ -154,7 +154,7 @@ The `graphqlHTTP` function accepts the following options:
   of resources consumed. This may be an async function. The function is
   given one object as an argument: `{ document, variables, operationName, result, context }`.
 
-- **`validationRules`**: Optional additional validation rules queries must
+- **`validationRules`**: Optional additional validation rules that queries must
   satisfy in addition to those defined by the GraphQL spec.
 
 - **`customValidateFn`**: An optional function which will be used to validate
@@ -207,7 +207,7 @@ the parameters:
   named operations.
 
 - **`raw`**: If the `graphiql` option is enabled and the `raw` parameter is
-  provided raw JSON will always be returned instead of GraphiQL even when
+  provided, raw JSON will always be returned instead of GraphiQL even when
   loaded from a browser.
 
 GraphQL will first look for each parameter in the query string of a URL:
@@ -216,23 +216,23 @@ GraphQL will first look for each parameter in the query string of a URL:
 /graphql?query=query+getUser($id:ID){user(id:$id){name}}&variables={"id":"4"}
 ```
 
-If not found in the query-string, it will look in the POST request body.
+If not found in the query string, it will look in the POST request body.
 
 If a previous middleware has already parsed the POST body, the `request.body`
 value will be used. Use [`multer`][] or a similar middleware to add support
 for `multipart/form-data` content, which may be useful for GraphQL mutations
 involving uploading files. See an [example using multer](https://github.com/graphql/express-graphql/blob/304b24b993c8f16fffff8d23b0fa4088e690874b/src/__tests__/http-test.js#L674-L741).
 
-If the POST body has not yet been parsed, express-graphql will interpret it
+If the POST body has not yet been parsed, `express-graphql` will interpret it
 depending on the provided _Content-Type_ header.
 
 - **`application/json`**: the POST body will be parsed as a JSON
   object of parameters.
 
-- **`application/x-www-form-urlencoded`**: this POST body will be
+- **`application/x-www-form-urlencoded`**: the POST body will be
   parsed as a url-encoded string of key-value pairs.
 
-- **`application/graphql`**: The POST body will be parsed as GraphQL
+- **`application/graphql`**: the POST body will be parsed as GraphQL
   query string, which provides the `query` parameter.
 
 ## Combining with Other Express Middleware
@@ -296,8 +296,6 @@ const { graphqlHTTP } = require('express-graphql');
 
 const app = express();
 
-app.use(session({ secret: 'keyboard cat', cookie: { maxAge: 60000 } }));
-
 const extensions = ({
   document,
   variables,
@@ -328,7 +326,7 @@ for example:
 
 ```js
 {
-  "data": { ... }
+  "data": { ... },
   "extensions": {
     "runTime": 135
   }
@@ -339,7 +337,7 @@ for example:
 
 GraphQL's [validation phase](https://graphql.github.io/graphql-spec/#sec-Validation) checks the query to ensure that it can be successfully executed against the schema. The `validationRules` option allows for additional rules to be run during this phase. Rules are applied to each node in an AST representing the query using the Visitor pattern.
 
-A validation rule is a function which returns a visitor for one or more node Types. Below is an example of a validation preventing the specific field name `metadata` from being queried. For more examples see the [`specifiedRules`](https://github.com/graphql/graphql-js/tree/master/src/validation/rules) in the [graphql-js](https://github.com/graphql/graphql-js) package.
+A validation rule is a function which returns a visitor for one or more node Types. Below is an example of a validation preventing the specific field name `metadata` from being queried. For more examples, see the [`specifiedRules`](https://github.com/graphql/graphql-js/tree/main/src/validation/rules) in the [graphql-js](https://github.com/graphql/graphql-js) package.
 
 ```js
 import { GraphQLError } from 'graphql';
@@ -424,14 +422,14 @@ Each release of `express-graphql` will be accompanied by an experimental release
 Community feedback on this experimental release is much appreciated and can be provided on the [PR for the defer-stream branch](https://github.com/graphql/express-graphql/pull/726) or the [GraphQL.js issue for feedback](https://github.com/graphql/graphql-js/issues/2848).
 
 [`graphql.js`]: https://github.com/graphql/graphql-js
-[`formaterror`]: https://github.com/graphql/graphql-js/blob/master/src/error/formatError.js
+[`formaterror`]: https://github.com/graphql/graphql-js/blob/main/src/error/formatError.js
 [graphiql]: https://github.com/graphql/graphiql
 [`multer`]: https://github.com/expressjs/multer
 [`express-session`]: https://github.com/expressjs/session
 
 # Contributing to this repo
 
-This repository is managed by EasyCLA. Project participants must sign the free ([GraphQL Specification Membership agreement](https://preview-spec-membership.graphql.org) before making a contribution. You only need to do this one time, and it can be signed by [individual contributors](http://individual-spec-membership.graphql.org/) or their [employers](http://corporate-spec-membership.graphql.org/).
+This repository is managed by EasyCLA. Project participants must sign the free [GraphQL Specification Membership agreement](https://preview-spec-membership.graphql.org) before making a contribution. You only need to do this one time, and it can be signed by [individual contributors](http://individual-spec-membership.graphql.org/) or their [employers](http://corporate-spec-membership.graphql.org/).
 
 To initiate the signature process please open a PR against this repo. The EasyCLA bot will block the merge if we still need a membership agreement from you.