Added dockerhub docs, centered readme logo

********* PEOPLE *************
Primary reviewer: @suntzu86 

Reviewers:

********* DESCRIPTION **************
Branch Name: sclark_341_docker_docs
Ticket(s)/Issue(s): Closes #341

********* TESTING DONE *************

make -B docs visual
Let's also link to the tag for this version, e.g.,
https://github.com/Yelp/MOE/releases/tag/v0.1.0

That'll show the changelog for this version (and also nicely displays previous versions with changes).