Checkin document pages (#1068)
Checkin document pages (#1068)

* checkin md doc files

* add some docs

* add more docs

* change the folder location

* fix unit test

* fix typos

* fix typo

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