Clarify accepted values for projectQuery (#950)

It's not clear from reading that this config supports endpoints other
than the `/projects` endpoint. This attempts to clarify.

Author: camdencheek

docs/admin/code_hosts/gitlab.mdx

@@ -44,7 +44,10 @@ Example config:
 There are three fields for configuring which projects are mirrored/synchronized:
 
 - [`projects`](/admin/code_hosts/gitlab#configuration): A list of projects in `{"name": "group/name"}` or `{"id": id}` format. The order determines the order in which we sync project metadata and is safe to change.
-- [`projectQuery`](/admin/code_hosts/gitlab#configuration): A list of strings with one pre-defined option (`none`), and/or an URL path and query that targets the [GitLab Projects API endpoint](https://docs.gitlab.com/ee/api/projects.html), returning a list of projects.
+- [`projectQuery`](/admin/code_hosts/gitlab#configuration): A list of strings. Accepted values include:
+  - The special value `none`, which will sync no repositories.
+  - Query parameters for the [GitLab Projects API endpoint](https://docs.gitlab.com/ee/api/projects.html). For example, `?archived=false`.
+  - A path and set of query parameters for any GitLab API endpoint that returns a list of repos. For example, `groups/mygroup/projects?visibility=public`.
 - [`exclude`](/admin/code_hosts/gitlab#configuration): A list of projects to exclude which takes precedence over the `projects`, and `projectQuery` fields. It has the same format as `projects`.
 
 ### Troubleshooting