Note GraphQL docs need update too

When adding fields to the GraphQL endpoint, you'll need to add them to
the docs as well. So mention the developer should run the designated
rake task for that.

doc/development/geo/framework.md

@@ -676,6 +676,12 @@ the Admin Area UI, and Prometheus!
    }
    ```
 
+1. Update the GraphQL reference documentation:
+
+   ```shell
+   bundle exec rake gitlab:graphql:compile_docs
+   ```
+
 Individual widget synchronization and verification data should now be available
 via the GraphQL API!