Fix docs for motion_primitive_controllers

[christophfroehlich]

The path to the readme was wrong, rendering the repository readme instead.

I also moved the parameter section to the rst for rendering the yaml files.

fyi @mathias31415

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.22%. Comparing base (3a8a9aa) to head (7c2cdf9).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1877   +/-   ##
=======================================
  Coverage   85.22%   85.22%           
=======================================
  Files         142      142           
  Lines       13735    13735           
  Branches     1191     1191           
=======================================
  Hits        11706    11706           
  Misses       1632     1632           
  Partials      397      397           

Flag	Coverage Δ
unittests	85.22% <ø> (ø)

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