Improved documentation

[sowbug]

It'd be helpful to state that <story> is the numerical story ID in Tracker. It'd also be great to include an example of a description field that works, so that people don't have to guess at the spacing etc.:

As a foo
I want bar
In order to baz

Scenario: Testing Pickler
  Given this is true
  When I do this
  And I do that
  Then that is true

[ivanoblomov]

Yes, this was definitely a key insight for me. Thanks!