[fyi] stubs for markdown were submitted to typeshed

[hauntsaninja]

Type stubs for this library were submitted to typeshed in python/typeshed#4426

You don't need to take any action, but:
a) If you wish to include type stubs as part of your package, we're happy to transfer them to this repo (or potentially aid with the addition of inline types)
b) If you want us to remove the stubs from typeshed, we will!