git.txt: remove stale comment regarding GIT_WORK_TREE Official support for specifying --work-tree/GIT_WORK_TREE without --git-dir/GIT_DIR was added with v1.7.4-rc3~2^2~2. Update description of GIT_WORK_TREE to reflect this. Signed-off-by: Chris Rorvick <chris@rorvick.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>