Write documentation

[MaximilienNaveau]

I need to write documentation on:

• The readme
• Check the output of the doxygen
• Use the breathing-cat package in order to export the doc in the ReadTheDoc layout?
• Document the equations and the implementation details of the LinearFeedbackController class.
• Document the API: ros params, topics, msgs exchanged etc.

[MaximilienNaveau]

https://github.com/orgs/agimus-project/projects/3/views/9?pane=issue&itemId=89307822