Abuse reports functionality is undocumented

Summary

Trying to point a user at GitLab's "Abuse Report" functionality, I discovered that we don't seem to have any documentation for this.

Steps to reproduce

https://www.google.com/search?q=abuse+site:docs.gitlab.com&ei=N6HYWuOvF6fPgAaVh5-YCQ&start=0&sa=N&biw=2560&bih=1305

What is the expected correct behavior?

We should have documentation covering this extremely important feature of GitLab. A screenshot of the feature I'm talking about:

Screenshot_from_2018-04-19_14-58-11

Possible fixes

Write documentation :D