Improving docs and onboarding

[tianyin]

Given that Acto is growing bigger with more folks involved like @whentojump and @ThrivikramanV, especially its aim for practicality, we should start to write some effective docs to make it easy to use and develop. It basically makes our own life easier.

This is particularly needed for presentations like KubeCon (with audience of hardcore K8s developers instead of academics who only read papers) and also an ambition is to make it a MP for 598/527.

@whentojump @ThrivikramanV Could you write down everything that took your time to figure out in the docs to benefit later students?

A obvious docs is needed for running Acto on CloudLab as we're pretty much relying on that now.