Python Client Documentation Tweaks

I found a few tweaks needed on the github page.

https://github.com/couchbase/couchbase-python-client

When trying to install Twisted.

1. When trying to run pip on a mac it may be required to run pip install --user <package> because of write permission in certain directories.

2. This error will occur after installing Twisted.

>>> from twisted.internet import reactor
:0: UserWarning: You do not have a working installation of the service_identity module: 'No module named service_identity'. Please install it from <https://pypi.python.org/pypi/service_identity> and make sure all of its dependencies are satisfied. Without the service_identity module and a recent enough pyOpenSSL to support it, Twisted can perform only rudimentary TLS client hostname verification. Many valid certificate/hostname mappings may be rejected.

The wheel file on this site needs to be run. https://pypi.python.org/packages/80/f5/8b1604e4d85ce60333a2fd4bc7b7743b21949b434b7c1c2c77eee9e7cd6f/service_identity-16.0.0-py2.py3-none-any.whl#md5=70eef3afd5e1294cb14a138d9ca5ec56

From https://pypi.python.org/pypi/service_identity#downloads

Otherwise every pip installation I used --user and worked successfully.