README: Point link to gerrit's bugtracker

README points to the github bugtracker, but that project is archived.

Update the link to gerrit's bugtracker, because gitiles is hosted
together with gerrit and both share many developers.

Change-Id: Ifb144062290f3e3c823717afd7266af90e69d27d
diff --git a/README.md b/README.md
index bdeba97..e33c15e 100644
--- a/README.md
+++ b/README.md
@@ -16,8 +16,7 @@
 
 ## Bugs
 
-Use the [issue tracker at github](https://github.com/google/gitiles/issues) to
-file bugs.
+Use [gerrit's issue tracker](https://issues.gerritcodereview.com/issues?q=status:open%20componentid:1370019&s=created_time:desc) to file bugs.
 
 ## Contributing to Gitiles