Add Twitter Badge to Readme Template

[osterman]

what

[![Twitter](https://img.shields.io/twitter/url/https/twitter.com/cloudposse.svg?style=social&label=Follow%20%40cloudposse)](https://twitter.com/cloudposse)

why

• Promote our Twitter account

[devsantiag]

good!!!

[osterman]

Closing as this repository is being deprecated. See #393 for details.