fix documentation for apply_force_at_point (local vs world space) (#430)

fix documentation for apply_force_at_point. 
fixes #428 

no code-changes at all, so no breaking changes.

---------

Co-authored-by: Joona Aalto <[email protected]>

Author: johannesvollmer

src/dynamics/rigid_body/forces.rs

@@ -154,7 +154,9 @@ impl ExternalForce {
         self
     }
 
-    /// Applies the given world-space `force` at a local `point`, which will also cause torque to be applied.
+    /// Applies the given `force` at the specified `point`, which will also cause torque to be applied.
+    ///
+    /// The force, point, and center of mass must be given in world space.
     pub fn apply_force_at_point(
         &mut self,
         force: Vector,
@@ -442,7 +444,9 @@ impl ExternalImpulse {
         self
     }
 
-    /// Applies the given world-space `impulse` at a local `point`, which will also cause an angular impulse to be applied.
+    /// Applies the given `impulse` at the specified `point`, which will also cause an angular impulse to be applied.
+    ///
+    /// The impulse, point, and center of mass must be given in world space.
     pub fn apply_impulse_at_point(
         &mut self,
         impulse: Vector,