[PaddleNLP 3.0] Update README

[DrownFish19]

PR types

Others

PR changes

Docs

Description

1. Update README.md and README_en.md.
2. Add markdownlint tool to format .md files.

[paddle-bot[bot]]

Thanks for your contribution!

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 55.42%. Comparing base (e336e78) to head (2e6b521). Report is 1 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #8681 +/- ## ======================================== Coverage 55.42% 55.42% ======================================== Files 626 626 Lines 98082 98082 ======================================== Hits 54364 54364 Misses 43718 43718 ```

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[ZHUI]

最新dev下面的文档软链接都丢失了。 https://github.com/PaddlePaddle/PaddleNLP/tree/develop/docs/llm

https://github.com/PaddlePaddle/PaddleNLP/tree/v2.8.1/docs/llm