fix documentation

[stevejpurves]

The docs are terrible, the README doesn;t even explain properly how to get started. Add / improve

• quick start section for getting running from dockerhub - with key commands
• getting start from this repo section - with key startup commands
• a section on customising the dockerfile
• how to contribute / add a package
• license

[stevejpurves]

this has been partially addressed here https://github.com/softwareunderground/subsurface-ml-docker

and we should open an updated issue over there