"gdk run thin" allows only one concurrent connection

In order to debug with pry I'm following the instructions here - https://gitlab.com/gitlab-org/gitlab-development-kit/blob/master/doc/howto/pry.md.

When I want to use GitLab UI to create / edit a file Thin blocks indefinitely. I think that it's because Thin process can handle only one concurrent connection. For committing to the repository with web UI we need at least two processes, because we hit our API from Git hooks. This second request is queued after the first request and the first request cannot complete.

Alternatives

1. Change gdk run thin to start two processes
2. (or at least) update the documentation to mention this caveat