update reference frames

Author: ufechner7

docs/src/reference_frames.md

@@ -23,11 +23,11 @@ This is a body-fixed reference frame.
 
 The origin of the kite reference frame can be defined by the user by calling the function `init_kp(origin::MVec3)` where the origin must be defined in the `CAD` reference frame.
 
-## The orientation of the kite
-For the orientation, either a quaternion or roll, pitch and yaw angles are used. The orientation is defined with respect to the NED (North, East, Down) reference frame.
+## The turn rates
+The turn rates $\mathrm{omega} = [\mathrm{omega_x}, \mathrm{omega_y} ,\mathrm{omega_z}]$ are defined in the **KP** reference frame. The unit of the components is $rad/s$-
 
 ## Input and output
-- when running a simulation, the orientation of the kite must be provided on each time step
+- when running a simulation, the turnrate of the kite must be provided on each time step
 - the apparent wind speed vector `v_a` is defined in the **KP** reference frame
 - the resulting forces are defined in the **KP** reference frame
 - the **CL**, **CD**, **CS** and the resulting moments and moment coefficients are defined in the **KP** reference frame