Add an example notebook for implementing PS with Ray  (#1522)
Add an example notebook for implementing PS with Ray  (#1522)

* upup

* add ps notebook for ray

yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL