Couchbase Python SDK - Update 3.x Python Compatibility

In the 3.0 - 3.2 Compatibility Docs, we should add a Python Version Compatibility section like we have in the 4.x version of the SDK. That way we clearly define what version of Python are supported (see compat docs here).

We should also remove the statement below from the compat docs.

The Python SDK 3.x requires Python 3, with Python 3.5 and above supported. Because the Python SDK is written primarily in C using the CPython API, the official SDK will not work on PyPy.

Please let us know if you require a PyPy-compatible version of the SDK.

We can add the PyPy statement to the Python Version Compatibility (should also add that in the 4.x compat docs).