add regularizer docs (#1308)
add regularizer docs (#1308)

revise doc
yiheng/BigDL,yiheng/BigDL,jenniew/BigDL,qiuxin2012/BigDL,zhangxiaoli73/BigDL,yiheng/BigDL,i8run/BigDL-1,luchy0120/BigDL,luchy0120/BigDL,wzhongyuan/BigDL,qiuxin2012/BigDL,jenniew/BigDL,luchy0120/BigDL,i8run/BigDL-1,zhangxiaoli73/BigDL,qiuxin2012/BigDL,wzhongyuan/BigDL,jenniew/BigDL,i8run/BigDL-1,wzhongyuan/BigDL,zhangxiaoli73/BigDL