fix(dist): add py.typed to package_data (#90)

Fixes #89, by adding `py.typed` to `package_data`, this was validated by running locally the following commands:

setup.py

@@ -24,7 +24,7 @@
     author_email="[email protected]",
     description="Pure python implementation of magic file detection",
     long_description=long_description,
-    package_data={"puremagic": ["*.json"]},
+    package_data={"puremagic": ["*.json", "py.typed"]},
     packages=["puremagic"],
     include_package_data=True,
     platforms="any",