Modernize documentation links

Summary:
  - Point them at the new Diviner.
  - Make them a little less cumbersome to write.

Test Plan: Found almost all of these links in the UI and clicked them.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D8553

src/applications/differential/controller/DifferentialDiffCreateController.php

@@ -41,8 +41,7 @@ final class DifferentialDiffCreateController extends DifferentialController {
     }
 
     $form = new AphrontFormView();
-    $arcanist_href = PhabricatorEnv::getDoclink(
-      'article/Arcanist_User_Guide.html');
+    $arcanist_href = PhabricatorEnv::getDoclink('Arcanist User Guide');
     $arcanist_link = phutil_tag(
       'a',
       array(