KAFKA-3164: Document client and mirrormaker upgrade procedure/require…
KAFKA-3164: Document client and mirrormaker upgrade procedure/require…

…ments

Author: Grant Henke <granthenke@gmail.com>

Reviewers: Gwen Shapira

Closes #838 from granthenke/upgrade-docs

racker/kafka,racker/kafka,racker/kafka,racker/kafka