Document that git-am can read standard input.
Document that git-am can read standard input.

Signed-off-by: Michael S. Tsirkin <255103e50249e3d658441816e0597170ebfc16ef@mellanox.co.il>
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