Update instructions to reflect Python 2.7 as many distros default to Python 3.x

[Luke-Tech]

Please update installation instructions to explicitly use Python 2.7 or update the code as there are some issues with running it under Python 3. Many distros default to Python 3.x.

Specify Python 2.7 when building the virtualenv:

virtualenv -p /usr/bin/python2.7 <env_name>

Thanks!

[manincharge]

It took me hours to figure out this. Instructions should be updated. Especially since the canary recommends 3.7+