Include information about Windows usage and Python/DB versions in README

[anorthall]

There has been at least two instances of confusion about the need to modify versions before running, so I thought I'd clarify it in README.md.

[sarahboyce]

LGTM ⭐

[anorthall]

I removed this because I tested the error and it is extremely specific and could not be confused - not necessary to have here.

[ngnpope]

I've just opened #48 which addresses a whole host of issues. In there I've removed the ${PWD} - I'm not honestly sure why it was added. It also makes the default for DJANGO_PATH equal to ./django which removes another thing that needs to be configured (as long as the django and django-docker-box repositories are cloned adjacent to each other).

Ideally I'd like to avoid adding a bunch of special instructions for different platforms if we can avoid it. Maybe instead of having to define DOCKER_DEFAULT_PLATFORM=linux/amd64 we could add platform: linux/amd64 in compose.yml and/or --platform=linux/amd64 to FROM in the Containerfile.