Adds git ssh section

Git operations via SSH are subject to
non-configurable rate limiting.

doc/security/rate_limits.md

@@ -70,6 +70,23 @@ For configuration information, see
 ## Non-configurable limits
+### Git operations via Shell (SSH)
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/78373) in GitLab 14.7.
+
+GitLab Shell performs rate-limiting by user account and project for Git operations. 
+GitLab Shell accepts `git` operation requests and then makes a call to the 
+Rails rate-limiter (backed by Redis).
+If the `user + project` exceeds the rate limit, GitLab Shell drops further
+connection requests for that `user + project`.
+
+The rate-limiter is applied at the Git command ([plumbing](https://git-scm.com/book/en/v2/Git-Internals-Plumbing-and-Porcelain)) level. 
+Each command has a rate limit of 600/minute. For example, 
+`git push` has 600/minute and `git pull` has another 600/minute.
+
+As the same commands are shared by `git-upload-pack`, `git pull` and `git clone`,
+they're in effect the same command for the purposes of rate-limiting.
+
 ### Repository archives
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/25750) in GitLab 12.9.