ADMIN: Example code into README
ADMIN: Example code into README

Demonstration code is now inserted. Syntax highlighting achieved
with .rst `.. code:: python` directive.

Also added:

 * Prelim `pip install tempvars` in anticipation of the beta
   release
 * Note that it's Py3 only
 * Add prelim link to docs

bskinn/tempvars,bskinn/tempvars