Improve documentation for setting up on Windows

[zerolab]

This has been a blocker during the Minsk sprint, and other cases too

[Meteor0id]

Also consider the bakery demo:
wagtail/bakerydemo#218

[Oghenekevbe]

When I tried to make migrations or running the server, I kept hitting dotenv errors
so I checked the pip list and saw that we had python-dotenv* and django-dotenv

Here is what I did.
After the fifth step, ( # 5. ssh into your new Vagrant virtual machine.
vagrant ssh)

I installed the requirements file which is located at wagtail-dev\vagrant-wagtail-develop\bakerydemo\requirements.txt

pip install -r requirements.txt

I uninstalled python-dotenv

pip uninstall python-dotenv

Then made migrations and ran my server

Maybe we can include that for those who decide to use the vagrant process