Update DEVELOPING.md
Update DEVELOPING.md

mention release notes in development guidelines.
Kwasniewski/Opentok-Java-SDK,drahot/Opentok-Java-SDK,Kwasniewski/Opentok-Java-SDK,opentok/Opentok-Java-SDK,opentok/Opentok-Java-SDK,drahot/Opentok-Java-SDK,mukesh-kum/Opentok-Java-SDK,mukesh-kum/Opentok-Java-SDK