Missing py.typed marker file for exporting type hinting

[gkoch78]

Package is using type hinting in its code, which is really great.
However, when using this package in my own application/package and running mypy on my code base, mypy complains the package does not export type hints.

Adding a py.typed marker file would allow mypy to recognize the type hints.
Details in here: https://peps.python.org/pep-0561/#packaging-type-information