Document n1ql REST API parameter auto-execute

6.5.0 sports a new feature called auto execute, whereby a prepared statement can be prepared and executed in a single step.
This is regarded as a feature for internal usage only - specifically, for the benefit of the SDKs.
This said, all of the n1ql REST API is documented, and it would probably help users understand better the inner working for the SDK / n1ql interaction if this was documented as well.