This should i.e. forbid crawlers to index all of the git diffs which
put's unneccessary load on the server and is not really of benefit to be
indexed anyways.

Link: archlinux/infrastructure#610


Reviewed-by: Sven-Hendrik Haase <svenstaro@gmail.com>
Reviewed-by: Levente Polyak <anthraxx@archlinux.org>
Signed-off-by: Christian Heusel <christian@heusel.eu>