added docs
added docs

jpellerin/PhysicsJS,Luwdo/PhysicsJS,VANITAX/PhysicsJS,VANITAX/PhysicsJS,Rawneed/PhysicsJS,eric-seekas/PhysicsJS,griever989/PhysicsJS,eric-seekas/PhysicsJS,rohit765/PhysicsJS,pietro909/PhysicsJS,mcanthony/PhysicsJS,Nayar/PhysicsJS,Luwdo/PhysicsJS,wellcaffeinated/PhysicsJS,haithemaraissia/PhysicsJS,pietro909/PhysicsJS,griever989/PhysicsJS,jpellerin/PhysicsJS,rohit765/PhysicsJS,mcanthony/PhysicsJS,Rawneed/PhysicsJS,haithemaraissia/PhysicsJS,Nayar/PhysicsJS,wellcaffeinated/PhysicsJS