Update docs to reflect new gem location

We should put new gems in https://gitlab.com/gitlab-org/ruby/gems/ to
make it easier to discover what gems we actually maintain or fork.

doc/development/gemfile.md

@@ -55,7 +55,7 @@ to a gem, go through these steps:
    - For an example, see the [merge request !57805](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/57805).
 1. Once the gem is stable - we have been using it in production for a
    while with few, if any, changes - extract to its own project under
-   the `gitlab-org` namespace.
+   the [`gitlab-org/ruby/gems` namespace](https://gitlab.com/gitlab-org/ruby/gems/).
        1. When creating the project, follow the [instructions for new projects](https://about.gitlab.com/handbook/engineering/#creating-a-new-project).
        1. Follow the instructions for setting up a [CI/CD configuration](https://about.gitlab.com/handbook/engineering/#cicd-configuration).
        1. Follow the instructions for [publishing a project](https://about.gitlab.com/handbook/engineering/#publishing-a-project).