Start of aws best practices docs

Disclaimer: I think the formatting is ok here (famous last words) 

This is a PR for a docs page which discusses some best practices and how-to for using Ansible with AWS. This should be a living document, we should encourage folks to add to this and share how they are using Ansible with AWS / a-n-other cloud (since majority of it is generic). I still need to add details on usage / use case for each module. I propose adding this information later once we find a place for this base document.