Add info about CardTransition in the module docstring.
Add info about CardTransition in the module docstring.

autosportlabs/kivy,inclement/kivy,manthansharma/kivy,bionoid/kivy,rnixx/kivy,KeyWeeUsr/kivy,janssen/kivy,janssen/kivy,akshayaurora/kivy,kived/kivy,inclement/kivy,akshayaurora/kivy,rnixx/kivy,tony/kivy,janssen/kivy,LogicalDash/kivy,jkankiewicz/kivy,jegger/kivy,akshayaurora/kivy,Cheaterman/kivy,autosportlabs/kivy,matham/kivy,manthansharma/kivy,KeyWeeUsr/kivy,jegger/kivy,LogicalDash/kivy,manthansharma/kivy,LogicalDash/kivy,Cheaterman/kivy,matham/kivy,janssen/kivy,KeyWeeUsr/kivy,rafalo1333/kivy,jegger/kivy,kived/kivy,bionoid/kivy,rafalo1333/kivy,jkankiewicz/kivy,kivy/kivy,rnixx/kivy,jegger/kivy,jkankiewicz/kivy,LogicalDash/kivy,bionoid/kivy,matham/kivy,rafalo1333/kivy,bionoid/kivy,autosportlabs/kivy,kivy/kivy,Cheaterman/kivy,matham/kivy,Cheaterman/kivy,tony/kivy,jkankiewicz/kivy,KeyWeeUsr/kivy,tony/kivy,inclement/kivy,manthansharma/kivy,kived/kivy,kivy/kivy