* modify readme

* modify readme

* modify readme

* modify readme

modify ernie_gen README (#5090)

* add ernie_gen

* optimize ernie_gen

* optimize ernie_gen

* optimize ernie_gen code

* fix crf bug

* add ernie_gen __init__.py

* modify nlp version

* fix ernie_gen predict

* optimize doc

add ernie_gen for the dygraph mode