Modify instructions; remove install script

Sorry to interfere, @crankycoder! I’ll avoid committing to this branch  after this!

I’d never used virtualenvwrapper before – it’s a cool thing. But I think we should leave it to the dev to decide if they want to use virtualenvwrapper or just virtualenv.

I’m also not keen on an install script… Just because doing it robustly involves quite a lot more code, and I don’t see much point in an install script if it’s not robust. Also, certain things are useful to introduce to the dev (e.g. running the webserver) so it’s better to get them running those commands manually.