update the readme for the word_embedding (#5050)

* add all wiki embedding and part of baidu encyclopedia embedding.

* add embedding example

* add people_daily, weibo, sougou pretrained embedding

* add zhihu, finacial,literature embedding

* Add embedding model readme; add embedding train example and readme

* fix README example

* fix embedding doc

* 1. move PAD to the end
2. Add Readme.md

* optimize readme doc

* Add TokenEmbedding

* download corpus embedding data
* load embedding data by specifying corpus name
* extend the vocab of tokenizer from corpus embedding data

* add unk token setting

* modify tokenizer

* add extend voacb

* move jieba tokenizer and rename corpus_name->embedding_name

* use bos url instead of localhost

* add log when loading data

* add token dot computation; add __repr__ of TokenEmbedding

* add color logging

* use paddlenlp.utils.log

* adjust repr

* update pretrained embedding table

* fix padding idx