Adds Phabricator documentation. This is a first step that answers many questions we have seen.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165736 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/DeveloperPolicy.rst b/docs/DeveloperPolicy.rst
index f940dbc..391b43a 100644
--- a/docs/DeveloperPolicy.rst
+++ b/docs/DeveloperPolicy.rst
@@ -137,6 +137,10 @@
 favor for someone else.  Note that anyone is welcome to review and give feedback
 on a patch, but only people with Subversion write access can approve it.
 
+There is a web based code review tool that can optionally be used
+for code reviews. See the documentation on `Code Reviews with
+Phabricator <Phabricator.html>`_.
+
 Code Owners
 -----------