Documentation: git-rev-list's "patterns"

git-rev-list(1) talks about patterns as values for the
--grep, --committed etc. parameters, without going into detail.
This patch mentions that these patterns are actually regexps.

Signed-off-by: Petr Baudis <pasky@suse.cz>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-rev-list.txt

@@ -193,12 +193,12 @@ limiting may be applied.
 --author='pattern', --committer='pattern'::
 
 	Limit the commits output to ones with author/committer
-	header lines that match the specified pattern.
+	header lines that match the specified pattern (regular expression).
 
 --grep='pattern'::
 
 	Limit the commits output to ones with log message that
-	matches the specified pattern.
+	matches the specified pattern (regular expression).
 
 --remove-empty::