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>

owners_client.py

@@ -182,4 +182,5 @@ def GetCodeOwnersClient(host, project, branch):
   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)

presubmit_canned_checks.py

@@ -1343,7 +1343,8 @@ def CheckOwnersFormat(input_api, output_api):
       output_api.PresubmitError(
           'code-owners is not enabled. Ask your host enable it on your gerrit '
           'host. Read more about code-owners at '
-          'https://gerrit.googlesource.com/plugins/code-owners.')
+          'https://chromium-review.googlesource.com/'
+          'plugins/code-owners/Documentation/index.html.')
   ]
 
 
@@ -1363,7 +1364,8 @@ def CheckOwners(
       output_api.PresubmitError(
           'code-owners is not enabled. Ask your host enable it on your gerrit '
           'host. Read more about code-owners at '
-          'https://gerrit.googlesource.com/plugins/code-owners.')
+          'https://chromium-review.googlesource.com/'
+          'plugins/code-owners/Documentation/index.html.')
   ]