Add connection type to $env

We could detect if it's wifi or 3g or lte, etc. and render completely different versions of an app if we wanted. Just need to add another attribute to [$env](http://docs.jasonette.com/env/)

Start with the linked $env documentation at docs.jasonette.com/env/ and inspect how existing environment attributes are described. Document the connection type values mentioned in the issue, including Wi-Fi, 3G, and LTE, and ensure the page explains how the new attribute can be used; the documentation is done when the attribute and its possible values are clear.

Written by the indexing model from the issue text.