From: Linus Arver <linusa@google.com>

Although we've had this script since 4d06402b1b (contrib: add
git-contacts helper, 2013-07-21), we don't mention it in our
introductory docs. Do so now.

Signed-off-by: Linus Arver <linusa@google.com>

Submitted-As: https://lore.kernel.org/git/pull.1704.git.1712017205754.gitgitgadget@gmail.com