scrooge: Update SBT Plugin Documentation
scrooge: Update SBT Plugin Documentation

Problem / Solution

The SBT Plugin documentation section for Scrooge refers
to outdated plugin, thrift, and library versions. It
also mentions some very old information about upgrading
versions. Let's give it an overhaul.

JIRA Issues: CSL-9064

Differential Revision: https://phabricator.twitter.biz/D397285

twitter/scrooge,twitter/scrooge,twitter/scrooge,twitter/scrooge