[Enhancement] Change readme style and Update metafiles. (#895)

* [Enhancement] Change readme style and prepare for metafiles update.

* Update apcnet github repo url.

* add code snippet.

* split code snippet & official repo.

* update md2yml hook.

* Update metafiles.

* Add converted from attribute.

* process conflict.

* Put defualt variable value.

* update bisenet v2 metafile.

* checkout to ubuntu environment.

* pop empty attribute & make task attribute list.

* update readme style

* update readme style

* update metafiles

Co-authored-by: Junjun2016 <hejunjun@sjtu.edu.cn>