Update README to show how to disable introspection

Author: danielrearden

README.md

@@ -308,6 +308,27 @@ export function DisallowMetadataQueries(context) {
 }
 ```
 
+### Disabling introspection
+
+Disabling introspection does not reflect best practices and does not necessarily make your
+application any more secure. Nevertheless, disabling introspection is possible by utilizing the
+`NoSchemaIntrospectionCustomRule` provided by the [graphql-js](https://github.com/graphql/graphql-js)
+package.
+
+```js
+import { specifiedRules, NoSchemaIntrospectionCustomRule } from 'graphql';
+
+app.use(
+  '/graphql',
+  graphqlHTTP((request) => {
+    return {
+      schema: MyGraphQLSchema,
+      validationRules: [...specifiedRules, NoSchemaIntrospectionCustomRule],
+    };
+  }),
+);
+```
+
 ## Other Exports
 
 **`getGraphQLParams(request: Request): Promise<GraphQLParams>`**