git-grep: document --and, --or, --not, ( and )
git-grep: document --and, --or, --not, ( and )

[jc: added an example section.]

Signed-off-by: Matthias Lederhofer <507cbf130ec1f0ec254653b4a9393a0899dd8ba7@gmx.net>
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