Added release notes for 3.1.2 release

Author: peakpg

doc/release_notes.txt

@@ -1,3 +1,11 @@
+v3.1.2
+
+This is a small release which fixes a serious security patch. It is highly recommended that users update to this version.
+
+Lighthouse ticket #'s:
+* #314 - Page Templates and Partials will now 'page' if there are > 15 of them.
+* #363 - Security patch that closes a security hole that would allow unauthorized users to delete portlets. Special thanks to Jan Schulz-Hofen for identifying the vulnerability and providing a patch for this.
+
 v3.1.0
 
 BrowserCMS 3.1 is done! The release has a few exciting new features/refinements as well as its share of bug fixes. As always, you can get it by running 'gem install browsercms', and follow the upgrade guide on the wiki. Please report any errors found to our bug tracking system: https://browsermedia.lighthouseapp.com/projects/28481-browsercms-30