first example usage

This will be a work-in-progress. It needs to:

* short enough to avoid TL;DR
* long enough to be meaningful
* convey our tone
* stand apart from the task timer crowd

We'll use text for now, but I bet we'd get a lot of mileage from
an animated GIF.
installation instructions
how to enable tab completion
tease plugins for OS X Reminders and Things.app
better language around finding tasks