add unit

Author: ufechner7

src/VortexStepMethod.jl

@@ -138,7 +138,7 @@ Union of different definitions of the aerodynamic properties of a wing section.
   - (`alpha_range`, `cl_vector`, `cd_vector`, `cm_vector`) for `POLAR_VECTORS`
   - (`alpha_range`, `beta_range`, `cl_matrix`, `cd_matrix`, `cm_matrix`) for `POLAR_MATRICES` 
 
-where `alpha` is the angle of attack, `beta` is trailing edge angle, `cl` the lift coefficient,
+where `alpha` is the angle of attack [rad], `beta` is trailing edge angle [rad], `cl` the lift coefficient,
 `cd` the drag coefficient and `cm` the pitching moment coefficient. The camber of a kite refers to 
 the curvature of its airfoil shape. The camber is typically measured as the maximum distance 
 between the mean camber line (the line equidistant from the upper and lower surfaces)