[doc] Update build badges on readme file. (#3235)
[doc] Update build badges on readme file. (#3235)

* [skip ci] Add a formal security disclosure section.

* [skip ci] Update links to docs and zh-Hans docs, also fix other broken links.

* [skip ci] Not sure what to do with the hub link, hide for now.

* [skip ci] Use formal words.

* [skip ci] Also update the PR template.

* Loosen the gitignore restrictions for docs folder.

* Add back the missing metadata and image for docs. Fixing https://github.com/taichi-dev/docs.taichi.graphics/pull/71.

* Remove references to API docs.

* This is dumb..

* Remove outdated badges and add a postsubmit check badge.

* Remove useless yarn lockfile.
yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi