Add testing section to README

This changeset adds a section on testing to the `README`. I try to run this locally before submitting PRs. It is pretty much exactly what Jenkins does as part of the PR and merge to `develop` builders.
Right now, it'll skip over the monitoring dependencies and adjust your Django settings module. You'd probably want to re-provision after with `VAGRANT_ENV` unset to reset your Django settings module.

For more detail, search the Ansible directory for `not_testing`. Those roles/tasks won't be re-applied. Also, look at `group_vars/test` to see Ansible variable differences vs. `group_vars/development`.