Update how to release document.
Add release version to getting started guide.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42454 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/GettingStarted.html b/docs/GettingStarted.html
index 874dc37..e2b07a6 100644
--- a/docs/GettingStarted.html
+++ b/docs/GettingStarted.html
@@ -707,6 +707,7 @@
   subdirectories of the '<tt>tags</tt>' directory:</p>
 
 <ul>
+<li>Release 2.1: <b>RELEASE_21</b></li>
 <li>Release 2.0: <b>RELEASE_20</b></li>
 <li>Release 1.9: <b>RELEASE_19</b></li>
 <li>Release 1.8: <b>RELEASE_18</b></li>