Update install docs for rpi.
Update install docs for rpi.

rnixx/kivy,matham/kivy,kivy/kivy,akshayaurora/kivy,kivy/kivy,rnixx/kivy,rnixx/kivy,inclement/kivy,matham/kivy,akshayaurora/kivy,inclement/kivy,kivy/kivy,matham/kivy,matham/kivy,inclement/kivy,akshayaurora/kivy