Add permission to create signed tags

Change-Id: Ib23f67a76ea4e77e4b0222ef23bf92be0cecece8
diff --git a/project.config b/project.config
index 1c9448c..930152c 100644
--- a/project.config
+++ b/project.config
@@ -13,6 +13,8 @@
 [access "refs/tags/*"]
 	createTag = group Project Owners
 	createTag = group gerrit-release-creators
+	createSignedTag = group Project Owners
+	createSignedTag = group gerrit-release-creators
 [access "refs/*"]
 	owner = group google/gerritcodereview-maintainers@googlegroups.com
 [receive]