Project is missing py.typed marker

[ssbarnea]

When adding the package, mypy complains about missing type marker.

src/mkdocs_ansible/__init__.py:10: error: Skipping analyzing "mkdocs_macros.plugin": module is installed, but missing library stubs or py.typed marker  [import-untyped]
src/mkdocs_ansible/__init__.py:10: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports

This can easily be sorted by just adding the py.typed inside the package, even before the full types are adopted by the project.