Document a failure mode for large repositories in Geo

Merged Nick Thomas requested to merge (removed):39977-git-timeout-for-geo-doc into master

What does this MR do?

Adds a caveat about Geo + large repositories to the troubleshooting document

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

We didn't manage to increase the default timeout in time for %10.2

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

Related to gitlab-ce#39977

Edited by 🤖 GitLab Bot 🤖