Documentation/config.txt: document mailinfo.scissors
Documentation/config.txt: document mailinfo.scissors

The variable was documented in git-mailinfo.txt, but not in config.txt.
The detailed documentation is still the one of --scissors in
git-mailinfo.txt, but we give enough information here to let the user
understand what it is about, and to make it easy to find it (e.g.
searching ">8" and "8<" finds it).

Signed-off-by: Matthieu Moy <d4d2cc2a6ec7b2aa587d4887cc5ed200f9b685a1@imag.fr>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

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