Grøstl Addendum

This document is an addendum to the submission document of Grøstl, which was selected for the second round of NIST's SHA-3 competition. We stress that we do not change the specification of Grøstl. In other words, Grøstl is defined exactly as specified in the original submission document. In this document we mention a few alternative descriptions of our SHA-3 candidate Grøstl and describe recent analysis results on Grøstl