Documentation update: Contribution guidelines

[paulgessinger]

• [x] CONTRIBUTING.rst remove style guide part + link to docs style guide

• 1525

  • [x] How to run the formatting (@AJPfleger)
  • [x] How to build the documentation (@paulgessinger)
  • [x] What is clang-tidy (@paulgessinger)
  • [x] What is physmon (@paulgessinger)
  • [x] What are root file hash checks (@paulgessinger)
  • [x] MyST markdown cheat sheet (@benjaminhuth)

[stale[bot]]

This issue/PR has been automatically marked as stale because it has not had recent activity. The stale label will be removed if any interaction occurs.

[AJPfleger]

@paulgessinger It looks to me, that we finished all tasks. Can we finish/close this project/issue? :)