Add a link from the LLVM release notes to the Clang release notes.

I suspect we could profitably remove/move some of the bullet points
under Clang here to the Clang notes in order to keep things clean on
both sides. Unless I hear objections I'll start doing that once folks
have read over the Clang notes a bit.

llvm-svn: 145340

llvm/docs/ReleaseNotes.html

@@ -94,8 +94,7 @@ Release Notes</a>.</h1>
    production-quality compiler for C, Objective-C, C++ and Objective-C++ on x86
    (32- and 64-bit), and for Darwin/ARM targets.</p>
 
-<p>In the LLVM 3.0 time-frame, the Clang team has made many improvements:</p>
-
+<p>In the LLVM 3.0 time-frame, the Clang team has made many improvements:
 <ul>
   <li>Greatly improved support for building C++ applications, with greater
       stability and better diagnostics.</li>
@@ -141,6 +140,9 @@ Release Notes</a>.</h1>
       interface, to improve the performance of code completion and the mapping
       from source locations to abstract syntax tree nodes.</li>
 </ul>
+For more details about the changes to Clang since the 2.9 release, see the
+<a href="http://clang.llvm.org/docs/ReleaseNotes.html">Clang release notes</a>
+</p>
 
 
 <p>If Clang rejects your code but another compiler accepts it, please take a