Clarified Collection.create documentation

## Description
In the current documentation for `Collection.create`, it is stated that `false` will be returned if model validation fails.

I've clarified that you must pass the `{validation: true}` option in order for `create` to return false if model validation fails.

Currently, unless a developer dives fairly deep into the code, it isn't clear from the documentation why `create` will return a model event if model validation fails.