Add Model Documentation to Guides

[magneticmg]

See: https://groups.google.com/forum/#!topic/nooku-framework/nPTivEl2V-c

Have a crafted response, but was too much for that specific question, but could be a good base for an Essentials version of model documentation.

https://docs.google.com/document/d/1RSvbeuQ6FaJOAtHK1vRPycPCbFXnlU3bzSS2TdYy6bk/edit

@johanjanssens the version you copied is closer to complete so it would be better in that GDoc.

also see:
http://laravel.com/docs/5.0/eloquent