Badges should reference main

Remove discord link as we will likely just support GitHub Discussions
only in the future.

README.md

@@ -19,10 +19,8 @@ Extension documentation is found here: https://facelessuser.github.io/pymdown-ex
 
 License is MIT.  See [LICENSE](https://github.com/facelessuser/pymdown-extensions/blob/master/LICENSE.md) for more info.
 
-[github-ci-image]: https://github.com/facelessuser/pymdown-extensions/workflows/build/badge.svg?branch=master&event=push
-[github-ci-link]: https://github.com/facelessuser/pymdown-extensions/actions?query=workflow%3Abuild+branch%3Amaster
-[discord-image]: https://img.shields.io/discord/678289859768745989?logo=discord&logoColor=aaaaaa&color=mediumpurple&labelColor=333333
-[discord-link]:https://discord.gg/TWs8Tgr
+[github-ci-image]: https://github.com/facelessuser/pymdown-extensions/workflows/build/badge.svg?branch=main&event=push
+[github-ci-link]: https://github.com/facelessuser/pymdown-extensions/actions?query=workflow%3Abuild+branch%3Amain
 [codecov-image]: https://img.shields.io/codecov/c/github/facelessuser/pymdown-extensions/main.svg?logo=codecov&logoColor=aaaaaa&labelColor=333333
 [codecov-link]: https://codecov.io/github/facelessuser/pymdown-extensions
 [pypi-image]: https://img.shields.io/pypi/v/pymdown-extensions.svg?logo=pypi&logoColor=aaaaaa&labelColor=333333