Show output of "git describe" in fotter

Merged username-removed-25042 requested to merge pserwylo/fdroid-website:git-info into master

If you are on the latest (annotated or signed) tag, then it will just show the tag. Otherwise, it shows [most recent tagtag]-[commits ahead of this tag]-g[current-commit-hash]. It also links to the relevant gitlab page to display that versions source code.