DOC: updated simple visualization example. Needs more text.
DOC: updated simple visualization example. Needs more text.

nilgoyyou/dipy,nilgoyyou/dipy,villalonreina/dipy,JohnGriffiths/dipy,JohnGriffiths/dipy,matthieudumont/dipy,StongeEtienne/dipy,StongeEtienne/dipy,FrancoisRheaultUS/dipy,FrancoisRheaultUS/dipy,matthieudumont/dipy,villalonreina/dipy