Merge branch 'mjang-graphql-howto-use-schema-link' into 'master'

Add info / link from GraphQL pages to doc / schema generation

See merge request gitlab-org/gitlab!42516

doc/api/graphql/index.md

@@ -113,3 +113,11 @@ Machine-readable versions are also available:
 
 - [JSON format](reference/gitlab_schema.json)
 - [IDL format](reference/gitlab_schema.graphql)
+
+## Generate updates for documentation
+
+If you've changed the GraphQL schema, you should set up an MR to gain approval of your changes.
+To generate the required documentation and schema, follow the instructions given in the
+[Rake tasks for developers](../../development/rake_tasks.md#update-graphql-documentation-and-schema-definitions) page.
+
+Be sure to run these commands using the [GitLab Development Kit](https://gitlab.com/gitlab-org/gitlab-development-kit/).