Support refspecs in about-filter.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgitrc.5.txt

@@ -371,7 +371,9 @@ repo.path::
 
 repo.readme::
 	A path (relative to <repo.path>) which specifies a file to include
-	verbatim as the "About" page for this repo. Default value: none.
+	verbatim as the "About" page for this repo. You may also specify a
+	git refspec by head or by hash by prepending the refspec followed by
+	a colon. For example, "master:docs/readme.mkd" Default value: none.
 
 repo.snapshots::
 	A mask of allowed snapshot-formats for this repo, restricted by the