ISSUE #336: add DC/OS package update and instructions
ISSUE #336: add DC/OS package update and instructions

Descriptions of the changes in this PR:

Provide instructions of updating DCOS package by using latest docker image when do new release.

Master Issue: #336

Author: Jia Zhai <zhaijia@apache.org>

Reviewers: Sijie Guo <sijie@apache.org>

This closes #1247 from jiazhai/issue_336, closes #336

sijie/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,apache/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,sijie/bookkeeper,apache/bookkeeper,apache/bookkeeper,apache/bookkeeper,ivankelly/bookkeeper,apache/bookkeeper,sijie/bookkeeper,apache/bookkeeper,sijie/bookkeeper,ivankelly/bookkeeper,ivankelly/bookkeeper