docs: Add to README note on best practices: i.e. - using virtualenv for python projects about services-test

[rpappalax]

good catch. I was thinking yesterday whether we should schedule a team mtg to standardize some things around automation. we already decided on some last year, but a lot of water has gone under the bridge.

[pdehaan]

Long story longer, here was the greps I needed to run autopep8 locally against the services-test repo:

$ autopep8 -r --diff --exclude=**/venv/*,./kinto/bin/*,./kinto/lib/*,**/*.sikuli/*,./loop/e2e-test/marionette_env/*,**/node_modules/*,**/*.bak .

I'm sure this would be worse if I was working on a few other projects and happened to have more virtualenvs.

[rpappalax]

I think we'll have to address this on a project-by-project basis as a best practice. This should probably be something added to the README. I'll change the issue title accordingly.

[rpappalax]

this is really a best practice for python in general, but still we should add this on a per-project basis so going to close this issue (which is more directed at the over-arching README for all of services-test)