Update comment on gitweb_check/get_feature

This is taken from a patch from Giuseppe but unfortunately it came
too late to replace the series that was already on "next".  The comment
he updated here is better than the version we had previously, so I am
cherry-picking this bit not to lose it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

@@ -190,7 +190,9 @@ our %feature = (
 	# if there is no 'sub' key (no feature-sub), then feature cannot be
 	# overriden
 	#
-	# use gitweb_check_feature(<feature>) to check if <feature> is enabled
+	# use gitweb_get_feature(<feature>) to retrieve the <feature> value
+	# (an array) or gitweb_check_feature(<feature>) to check if <feature>
+	# is enabled
 
 	# Enable the 'blame' blob view, showing the last commit that modified
 	# each line in the file. This can be very CPU-intensive.