add python3 create rpm command in package section

[cookie33]

Hi,

I made a rpm:

python3 setup.py bdist_rpm

Afterwards it was installed with yum or rpm on Centos7. It is than in:

# rpm -ql b2handle | head
/usr/lib/python3.6/site-packages/b2handle-1.1.2-py3.6.egg-info/PKG-INFO
/usr/lib/python3.6/site-packages/b2handle-1.1.2-py3.6.egg-info/SOURCES.txt
/usr/lib/python3.6/site-packages/b2handle-1.1.2-py3.6.egg-info/dependency_links.txt
/usr/lib/python3.6/site-packages/b2handle-1.1.2-py3.6.egg-info/not-zip-safe
/usr/lib/python3.6/site-packages/b2handle-1.1.2-py3.6.egg-info/requires.txt
/usr/lib/python3.6/site-packages/b2handle-1.1.2-py3.6.egg-info/top_level.txt
/usr/lib/python3.6/site-packages/b2handle/__init__.py
/usr/lib/python3.6/site-packages/b2handle/__pycache__/__init__.cpython-36.opt-1.pyc
/usr/lib/python3.6/site-packages/b2handle/__pycache__/__init__.cpython-36.pyc
/usr/lib/python3.6/site-packages/b2handle/__pycache__/clientcredentials.cpython-36.opt-1.pyc

You need to add/install python36-future to get it working. Can these things be added to the documentation?