Add beta notice to the GraphQL Guide (#659)

* Add beta notice to the GraphQL Guide

* Add beta notice

Author: davimacedo

_includes/graphql/getting-started.md

@@ -13,6 +13,7 @@ $ parse-server --appId APPLICATION_ID --masterKey MASTER_KEY --databaseURI mongo
 Notes:
 * Run `parse-server --help` or refer to [Parse Server Options](https://parseplatform.org/parse-server/api/master/ParseServerOptions.html) for a complete list of Parse Server configuration options.
 * ⚠️ Please do not use `--mountPlayground` option in production as anyone could access your API Playground and read or change your application's data. [Parse Dashboard](#running-parse-dashboard) has a built-in GraphQL Playground and it is the recommended option for production apps.
+* ⚠️ The Parse GraphQL ```beta``` implementation is fully functional but discussions are taking place on how to improve it. So new versions of Parse Server can bring breaking changes to the current API.
 
 After running the CLI command, you should have something like this in your terminal:
 

graphql.md

@@ -4,7 +4,7 @@ permalink: /graphql/guide/
 layout: guide
 platform: graphql
 language: graphql
-display_platform: GraphQL
+display_platform: GraphQL (beta)
 
 redirect_from:
   - /graphql/