Documentation: git-add -- do not say "cache", add examples.
Documentation: git-add -- do not say "cache", add examples.

Its use of git-ls-files --others is very nice, but sometimes gives
surprising results, so we'd better talk about it.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git