Wrong parameter type in centroidal MPC documentation

[Carlotta Sartore]

The documentation for the centroidal mpc parameter has some issues (at least if one want to set the parameter via code rather than via conf file):

bipedal-locomotion-framework/src/ReducedModelControllers/include/BipedalLocomotion/ReducedModelControllers/CentroidalMPC.h

Lines 70 to 71 in 9a25588

      * |         `sampling_time`         |     `double`     |                                                                                   Sampling time of the MPC.                                                                                  |    Yes    | 
      * |          `time_horizon`         |     `double`     |                                            The time horizon of the MPC. The number of knots will be given by `floor(time_horizon / sampling_time)`                                           |    Yes    | 

the time_horizon and sampling_time variable are datetime rather than double.

In addition, the unit is missing (I assume they are seconds).

@GiulioRomualdi if you want (and agree) I can fix them either in #650 or open a new PR ! Let me know

[Giulio Romualdi]

You can open a PR! Thank you 😀