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 a virtualenv, 
or install globally. If they use virtualenv anyway, they’ll know how to 
install, so I don’t think the install script is necessary.

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.