Clarify Bullet 2.x release procedure

git-svn-id: http://bullet.googlecode.com/svn@2646 08e121b0-ae19-0410-a57b-3be3395fd4fd
Releasing, add files that contain VERSION information for a release and remind to cr-create serialization data structure file 

git-svn-id: http://bullet.googlecode.com/svn@2647 08e121b0-ae19-0410-a57b-3be3395fd4fd