docs(): update, add graphql migration guide

Author: kamilmysliwiec

content/migration.md

@@ -36,3 +36,9 @@ To learn more, check out these articles: [Socket.io 3 Release](https://socket.io
 #### `@nestjs/config` package
 
 There was a minor breaking change in the `registerAs` function (typings), you can see what has changed in [this PR](https://github.com/nestjs/config/pull/173).
+
+#### `@nestjs/graphql` package
+
+There might be some small differences in how your auto-generated schema file may look like (changed types order). Also, if you use the schema-first approach, the automatically generated type definitions will change as there was a new `Nullable<T>` type introduced in the latest release.
+
+Also, all `HttpException` errors thrown from your resolvers will be now automatically mapped to the corresponding `ApolloError` instances, unless you set the `autoTransformHttpErrors` configuration property (in the options object you pass into the `GraphQLModule#forRoot()` method) to `false`.

content/techniques/http-module.md

@@ -2,7 +2,7 @@
 
 [Axios](https://github.com/axios/axios) is richly featured HTTP client package that is widely used. Nest wraps Axios and exposes it via the built-in `HttpModule`. The `HttpModule` exports the `HttpService` class, which exposes Axios-based methods to perform HTTP requests. The library also transforms the resulting HTTP responses into `Observables`.
 
-> info **Hint** You can also directly use any general purpose Node.js HTTP client library, including [got](https://github.com/sindresorhus/got) or [undici](https://github.com/nodejs/undici).
+> info **Hint** You can also use any general purpose Node.js HTTP client library directly, including [got](https://github.com/sindresorhus/got) or [undici](https://github.com/nodejs/undici).
 
 #### Installation