Add doc section about use outside of controllers.

See gh-98 for a discussion on this.
Update README.rdoc

Add a note about securing ActiveRecord resources by default, as an alternative to having to make sure each model is protected.
Update README.rdoc

As requested, spelling Active Record as a word, not the model.
Merge pull request #100 from bryanrite/patch-1

Update README.rdoc
Add usage example for use outside controllers
Merge pull request #99 from bemurphy/outside_controller_doc

Add doc section about use outside of controllers.
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