Add py.typed (#11865)

public/__init__.py

@@ -2,6 +2,6 @@
 from pathlib import Path
 
 
-def where():
+def where() -> Path:
     """Return path to the frontend."""
     return Path(__file__).parent

setup.cfg

@@ -19,3 +19,8 @@ python_requires = >= 3.4.0
 [options.packages.find]
 include =
     hass_frontend*
+
+[mypy]
+python_version = 3.4
+show_error_codes = True
+strict = True