After looking the git-tag manpage, someone on #git wondered how
to tag a commit that is not a branch head. This patch changes
the synopsis to say "<commit> | <object>" instead of "<head>" to
address his question.
Samuel Bronson had the idea of putting "<commit> | <object>"
for "<object>" because most tags point to commits (and for the
rest of the manpage, all tags point to commits).
Signed-off-by: Jonathan Nieder <jrnieder@uchicago.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>