Update code-owners documentation links

Bug: 1223715
Change-Id: Ia4cfaf6c421432f0b64662ab02bc4041f32173d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4585553
Auto-Submit: Gavin Mak <gavinmak@google.com>
Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>
Reviewed-by: Aravind Vasudevan <aravindvasudev@google.com>
diff --git a/owners_client.py b/owners_client.py
index 90de554..cf5fb3c 100644
--- a/owners_client.py
+++ b/owners_client.py
@@ -182,4 +182,5 @@
   raise Exception(
       'code-owners plugin is not enabled. Ask your host admin to enable it '
       'on %s. Read more about code-owners at '
-      'https://gerrit.googlesource.com/plugins/code-owners.' % host)
+      'https://chromium-review.googlesource.com/'
+      'plugins/code-owners/Documentation/index.html.' % host)