Documentation for autoCreatedAt and autoCreatedAt

In some cases Waterline shouldn't create "createdAt" and "updatedAt" properties automatically. The reference for prevent this behaviour was missing in README.md.
Documentation for autoPK

Documenting the model property autoPK. If you don't need an id
property as an auto incrementing index, you should override it or
set autoPK to false.
Fix at autoPK property description
Merge pull request #114 from murilopolese/patch-1

Documentation for autoCreatedAt and autoUpdatedAt