Add 2.3 release tag.

llvm-svn: 52122

Author: tlattner

llvm/docs/GettingStarted.html

@@ -716,6 +716,7 @@
   subdirectories of the '<tt>tags</tt>' directory:</p>
 
 <ul>
+<li>Release 2.3: <b>RELEASE_23</b></li>
 <li>Release 2.2: <b>RELEASE_22</b></li>
 <li>Release 2.1: <b>RELEASE_21</b></li>
 <li>Release 2.0: <b>RELEASE_20</b></li>