All `.. code::` instances have been changed to use `.. code-block::`,
and have been properly formatted. The syntax names have been normalised,
so all django templates use the `html+django` syntax, shell commands use
`sh`, and plain text uses `text`.
* State the requirement for Node.js up-front (since it's required by everyone, not just front-end devs)
* Point to vagrant-wagtail-develop instead of making people set up a Vagrant instance manually
* No need to fiddle with python paths via local.py - 'setup.py develop' handles that
* Skip instructions for virtualenvs (anyone who decides against the Vagrant route is expected to know how to use them)
