add a precision about the intended use of the ConcavePolygonShape
add a precision about the intended use of the ConcavePolygonShape

(cherry picked from commit 222a934e608640c598cc0f99780a74d66b5ac556)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot