Detailed documentation

[ggalgoczi]

Create detailed documentation for users / developers. Has to include:

• Prereqs
• Was to install/run (docker container, source, python(?))
• Supported physics
• Examples, including the raindrop geometry, performance quantification, validation script, profiling
• How to define geometry
• HPC + containers recipes
• Troubleshooting / FAQ

[ggalgoczi]

@plexoos let me know if I missed something.

[ggalgoczi]

Opened a branch called readthedocs. Added the current README. Will update. I was trying to set up automatic publishing on the readthedocs.org website. However I do not have access right to add the webhook, @plexoos do you agree to publish there?