WavefunctionSimulator should be imported from pyquil.api

[bramathon]

Issue Description

In the documentation, WavefunctionSimulator is imported from pyquil

https://pyquil-docs.rigetti.com/en/stable/basics.html#defining-parametric-gates

However, the WavefunctionSimulator must be imported from pyquil.api

How to Reproduce

from pyquil import WavefunctionSimulator

Environment Context

Tested in QCS pyquil v3.0.0