doc: use linkgit macro where needed.

Signed-off-by: NJean-Noël Avila <jn.avila@free.fr>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-grep.txt

@@ -209,7 +209,7 @@ providing this option will cause it to die.
 	Use \0 as the delimiter for pathnames in the output, and print
 	them verbatim. Without this option, pathnames with "unusual"
 	characters are quoted as explained for the configuration
-	variable core.quotePath (see git-config(1)).
+	variable core.quotePath (see linkgit:git-config[1]).
 
 -o::
 --only-matching::