DOC: fix docstring for flag checking
DOC: fix docstring for flag checking

Update docstring for new API.

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