Improve docs (overview)

[rdnfn]

Problem

The documentation can always be improved.

Solution

Add the following parts and improvements to the docs:

• Env list
  • Add more info to gym intergration specific config arguments to docs #38 (priority)
  • Add observation and action spaces to env list in docs #42
  • Add citation to gym integration readme pages #45
• Other
  • Create general yaml config documentation #78 (priority)
  • Fix API section in docs #37
  • Add advanced usage guide on wrappers #73
  • Add section on managing docker disk usage #69
  • remove/update old advanced usage guides #76
  • Add guide on using RLlib agents to docs #75
  • Add building illustration to main readme #79

For the first three issues it is important to setup a solid parsing pipeline from google drive and beobench_contrib repo. Further each integration should have its own page to make the pages more readable with one overview page with full env list.