docs: fix Discord links (#705)

README.md

@@ -31,6 +31,7 @@
 [![All Contributors][all-contributors-badge]](#contributors)
 [![PRs Welcome][prs-badge]][prs]
 [![Code of Conduct][coc-badge]][coc]
+[![Discord][discord-badge]][discord]
 
 [![Watch on GitHub][github-watch-badge]][github-watch]
 [![Star on GitHub][github-star-badge]][github-star]
@@ -295,5 +296,7 @@ Contributions of any kind welcome!
 [requests]: https://github.com/testing-library/user-event/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc+label%3Aenhancement
 [good-first-issue]: https://github.com/testing-library/user-event/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc+label%3Aenhancement+label%3A%22good+first+issue%22
 [fire-event]: https://testing-library.com/docs/dom-testing-library/api-events#fireevent
+[discord-badge]: https://img.shields.io/discord/723559267868737556.svg?color=7389D8&labelColor=6A7EC2&logo=discord&logoColor=ffffff&style=flat-square
+[discord]: https://discord.gg/testing-library
 [stackoverflow]: https://stackoverflow.com/questions/tagged/user-event
 <!-- prettier-ignore-end -->