Update releaes note.

Update version

Add electra modules (PaddlePaddle#1173)

* Add electra modules

* Amend module versions of chinese-bert-wwm, chinese-bert-wwm-ext, rbt3 and rbtl3

* Updata demo README.md

Add thanks

Update installation.md

Update sentence_sim.md

 add unitest, config, fix ernie_gen bugs and add ernie_tiny_couplet (P…

…addlePaddle#782)

Update release.md

modify_readme_contents,test=develop (PaddlePaddle#480)

update cmd_intro doc (hub download) (PaddlePaddle#453)

update cmd_intro doc (hub download)