DOC - added mention of optimized routine in python version
DOC - added mention of optimized routine in python version

nilgoyyou/dipy,maurozucchelli/dipy,oesteban/dipy,oesteban/dipy,StongeEtienne/dipy,matthieudumont/dipy,beni55/dipy,nilgoyyou/dipy,samuelstjean/dipy,samuelstjean/dipy,maurozucchelli/dipy,sinkpoint/dipy,rfdougherty/dipy,FrancoisRheaultUS/dipy,beni55/dipy,Messaoud-Boudjada/dipy,samuelstjean/dipy,jyeatman/dipy,rfdougherty/dipy,jyeatman/dipy,villalonreina/dipy,sinkpoint/dipy,demianw/dipy,matthieudumont/dipy,JohnGriffiths/dipy,StongeEtienne/dipy,Messaoud-Boudjada/dipy,mdesco/dipy,demianw/dipy,mdesco/dipy,villalonreina/dipy,FrancoisRheaultUS/dipy,JohnGriffiths/dipy,maurozucchelli/dipy