Document a couple more functions and the flags argument as used by
hold_lock_file_for_update() and hold_lock_file_for_append().
Reorganize the document to make it more accessible.
Helped-by: Jonathan Nieder <jrnieder@gmail.com>
Helped-by: Junio Hamano <gitster@pobox.com>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>