Harmonize documentation between pyfar packages

[f-brinkmann]

• [x] common contribution guidelines in gallery (#51)
• [x] help section in gallery (#51)
• [ ] individual installation guides / readmes per package via cookiecutter (@ahms5)
  • [ ] pyfar (https://github.com/pyfar/pyfar/pull/590)
  • [ ] sofar
  • [ ] spharpy
• [ ] remove concepts in pyfar (https://github.com/pyfar/pyfar/pull/591)
• [ ] remove examples
  • [x] pyfar (https://github.com/pyfar/pyfar/pull/574)
  • [ ] sofar
  • [ ] spharpy
• [ ] add code of conduct in gallery
• [ ] citation cff files per package

[sikersten]

We discussed that the contribution guidelines could be split at "Pull Request Guidlines".

[sikersten]

Remove section "Contributing" in Readmes

[pingelit]

Example for CODE_OF_CUNDUCT: https://www.contributor-covenant.org/