add py.typed so that your type annotations can inform application codebases

[petergaultney]

If you add a py.typed file to your source code root, then applications that people build will be able to have mypy and friends check that they're using your APIs basically correctly. This is pretty easy to do and since you're already doing a great job of putting type annotations in your code, it's likely this would be an improvement for lots of users!

[falkoschindler]

Sounds great, @petergaultney! We haven't been aware of py.typed, but we love to improve support for type annotations wherever we can. Would you like to create a pull request? 🙂

[petergaultney]

happy to!

#2142

[petergaultney]

closed by #2142 !