build: add missing bits to support typing

Author: guludo

CHANGELOG.md

@@ -7,7 +7,8 @@ Changelog](https://keepachangelog.com/en/1.0.0/), and this project adheres to
 
 
 ## Unreleased
-- Nothing yet.
+### Fixed
+- Added missing bits to support typing.
 
 ## 0.2.0 - 2021-12-09
 ### Added

setup.py

@@ -22,6 +22,9 @@
     long_description_content_type='text/x-rst',
     url='https://github.com/guludo/python-argparse-subdec',
     packages=['argparse_subdec'],
+    package_data={
+        'argparse_subdec': ['py.typed'],
+    },
     extras_require=extras_require,
     classifiers=[
         'Development Status :: 4 - Beta',