DOC: minor change for rendering the tutorial
DOC: minor change for rendering the tutorial

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