Update howto update GraphQL doc schema

doc/development/rake_tasks.md

@@ -276,8 +276,13 @@ In its current state, the Rake task:
 This uses some features from `graphql-docs` gem like its schema parser and helper methods.
 The docs generator code comes from our side giving us more flexibility, like using Haml templates and generating Markdown files.
 
-To edit the template used, please take a look at `lib/gitlab/graphql/docs/templates/default.md.haml`.
-The actual renderer is at `Gitlab::Graphql::Docs::Renderer`.
+To edit the content, you may need to edit the following:
+
+- The template. You can edit the template at `lib/gitlab/graphql/docs/templates/default.md.haml`.
+  The actual renderer is at `Gitlab::Graphql::Docs::Renderer`.
+- The applicable `description` field in the code, which
+  [Updates machine-readable schema files](#update-machine-readable-schema-files),
+  which is then used by the `rake` task described earlier.
 
 `@parsed_schema` is an instance variable that the `graphql-docs` gem expects to have available.
 `Gitlab::Graphql::Docs::Helper` defines the `object` method we currently use. This is also where you