Documentation for Conventions for organizing iidy

[rymndhng]

Given all the features in iidy, it'd be good to have a succinct document that highlights the conventions to recommend users of iidy:

Some things I can think of:

• naming of stack-args file name(stack-args.yml, stack-args.yaml)
• how to make stack-args.yml reusable
  • making use of -e or for multi-environment setups
• conventions for working with Templates (i.e. name them some-resource-template.yaml)

[tavisrudd]

The examples/ folder shows some basic conventions. We should add some examples that demonstrate the environments functionality and improve the README docs for that.