Update documentation for module

Added the new options to the example configuration file and added some
notes for the new configuration options:

- address: Select which address of the instance you want to use as the
  host address, or the address that Shinken will use to access it
- use_tags: EC2 tags that should be used as templates. The default is
  'use' and the format of the template names should be key:value. This
  allows us to use more than one template per host, and additional
  flexibility.

Also added documentation for 'regions' since it wasn't present at the,
though it works.