maint: Include top-level *.rst files early in git diff

We are converting more doc files to *.rst rather than *.texi. Most
doc files are already listed early in diffs due to our catchall
docs/*, but a few top-level files get missed by that glob.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20200220162214.3474280-1-eblake@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>