Update release notes (check SVN commit-after-approval access)

[benhamilton]

Summary

I was just granted commit-after-approval access to SVN,
and @clattner recommended I try a test commit.

So, this tweaks the release notes as a test.

[hokein]

LGTM.

clang-tools-extra/trunk/docs/ReleaseNotes.rst

 --------------------------
 
 - New module `objc` for Objective-C style checks.
 
 - New `objc-forbidden-subclassing
   <http://clang.llvm.org/extra/clang-tidy/checks/objc-forbidden-subclassing.html>`_ check
 
   Ensures Objective-C classes do not subclass any classes which are
-  not intended to be subclassed.
+  not intended to be subclassed. Includes a list of classes from Foundation
+  and UIKit which are documented as not supporting subclassing.
 
 - Renamed checks to use correct term "implicit conversion" instead of "implicit
   cast" and modified messages and option names accordingly:
 
     * **performance-implicit-cast-in-loop** was renamed to
       `performance-implicit-conversion-in-loop
       <http://clang.llvm.org/extra/clang-tidy/checks/performance-implicit-conversion-in-loop.html>`_
     * **readability-implicit-bool-cast** was renamed to