Update save_load.py

Fixed variable name

update doc and  make gpu_id =0 by default in Dygraph  Branch

fix doc

update eng doc

update doc

fix gpu_id

Dygraph

fix doc of slim

fix rec slim model link

* add distributed training doc

* Update and rename distributd_training.md to distributed_training.md

pdserving support win and v0.6.0

fix slim doc

update pdserving

refine deploy slim

Update joinus.png