DOC: improve shape point docs

rocketpy/rocket/aero_surface/fins/free_form_fins.py

@@ -107,7 +107,8 @@ def __init__(
             geometry defining points. The point (0, 0) is the root leading edge.
             Positive x is rearwards, positive y is upwards (span direction).
             The shape will be interpolated between the points, in the order
-            they are given. The last point connects to the first point.
+            they are given. The last point connects to the first point, and
+            represents the trailing edge.
         rocket_radius : int, float
             Reference radius to calculate lift coefficient, in meters.
         cant_angle : int, float, optional