Docs: Corrects forward hardware interfaces & Contributing.md

[matthias-mayr]

• Corrects the main branch in contributing.md
• Corrects the docs of the position & velocity forward controller
• Adds forward_effort_controller to the usage documentation

I allowed maintainers to edit the branch that this is pulled from in case you have something more to change in this PR.

[urfeex]

Thanks a lot 🙏

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 15.29%. Comparing base (1b121b7) to head (e93d8dd).
⚠️ Report is 512 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##            main    #1569       +/-   ##
==========================================
+ Coverage   3.59%   15.29%   +11.70%     
==========================================
  Files         13       34       +21     
  Lines        947     3878     +2931     
  Branches     152      467      +315     
==========================================
+ Hits          34      593      +559     
- Misses       843     3268     +2425     
+ Partials      70       17       -53     

Flag	Coverage Δ
unittests	15.29% <ø> (+11.70%)	⬆️

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