docs: update readme with v3-beta notes

Author: KingDarBoja

Diff for: README.md

@@ -21,26 +21,58 @@ Adds GraphQL support to your Flask application.
 Just use the `GraphQLView` view from `flask_graphql`
 
 ```python
+from flask import Flask
 from flask_graphql import GraphQLView
 
-app.add_url_rule('/graphql', view_func=GraphQLView.as_view('graphql', schema=schema, graphiql=True))
+from schema import schema
+
+app = Flask(__name__)
+
+app.add_url_rule('/graphql', view_func=GraphQLView.as_view(
+    'graphql',
+    schema=schema,
+    graphiql=True,
+))
 
 # Optional, for adding batch query support (used in Apollo-Client)
-app.add_url_rule('/graphql/batch', view_func=GraphQLView.as_view('graphql', schema=schema, batch=True))
+app.add_url_rule('/graphql/batch', view_func=GraphQLView.as_view(
+    'graphql',
+    schema=schema,
+    batch=True
+))
+
+if __name__ == '__main__':
+    app.run()
 ```
 
-This will add `/graphql` and `/graphiql` endpoints to your app.
+This will add `/graphql` endpoint to your app and enable the GraphiQL IDE.
+
+### Special Note for Graphene v3
+
+If you are using the `Schema` type of [Graphene](https://github.com/graphql-python/graphene) library, be sure to use the `graphql_schema` attribute to pass as schema on the `GraphQLView` view. Otherwise, the `GraphQLSchema` from `graphql-core` is the way to go.
+
+More info at [Graphene v3 release notes](https://github.com/graphql-python/graphene/wiki/v3-release-notes#graphene-schema-no-longer-subclasses-graphqlschema-type) and [GraphQL-core 3 usage](https://github.com/graphql-python/graphql-core#usage).
+
+
+### Supported options for GraphQLView
 
-### Supported options
  * `schema`: The `GraphQLSchema` object that you want the view to execute when it gets a valid request.
- * `context`: A value to pass as the `context` to the `graphql()` function.
- * `root_value`: The `root_value` you want to provide to `executor.execute`.
+ * `context`: A value to pass as the `context_value` to graphql `execute` function. By default is set to `dict` with request object at key `request`.
+ * `root_value`: The `root_value` you want to provide to graphql `execute`.
  * `pretty`: Whether or not you want the response to be pretty printed JSON.
- * `executor`: The `Executor` that you want to use to execute queries.
  * `graphiql`: If `True`, may present [GraphiQL](https://github.com/graphql/graphiql) when loaded directly from a browser (a useful tool for debugging and exploration).
+ * `graphiql_version`: The graphiql version to load. Defaults to **"1.0.3"**.
  * `graphiql_template`: Inject a Jinja template string to customize GraphiQL.
+ * `graphiql_html_title`: The graphiql title to display. Defaults to **"GraphiQL"**.
  * `batch`: Set the GraphQL view as batch (for using in [Apollo-Client](http://dev.apollodata.com/core/network.html#query-batching) or [ReactRelayNetworkLayer](https://github.com/nodkz/react-relay-network-layer))
  * `middleware`: A list of graphql [middlewares](http://docs.graphene-python.org/en/latest/execution/middleware/).
+ * `encode`: the encoder to use for responses (sensibly defaults to `graphql_server.json_encode`).
+ * `format_error`: the error formatter to use for responses (sensibly defaults to `graphql_server.default_format_error`.
+ * `subscriptions`: The GraphiQL socket endpoint for using subscriptions in graphql-ws.
+ * `headers`: An optional GraphQL string to use as the initial displayed request headers, if not provided, the stored headers will be used.
+ * `default_query`: An optional GraphQL string to use when no query is provided and no stored query exists from a previous session. If not provided, GraphiQL will use its own default query.
+* `header_editor_enabled`: An optional boolean which enables the header editor when true. Defaults to **false**.
+* `should_persist_headers`:  An optional boolean which enables to persist headers to storage when true. Defaults to **false**.
 
 You can also subclass `GraphQLView` and overwrite `get_root_value(self, request)` to have a dynamic root value
 per request.