📝 Add a license section to the README

Author: webknjaz

README.md

@@ -1,3 +1,12 @@
 # `re-actors/checkout-python-sdist@release/v1`
 
 A GitHub Action to unpack a source distribution package (tarball / `.tar.gz`) into the current workspace
+
+
+## License
+
+The contents of this project is released under the
+[BSD 3-clause license].
+
+
+[BSD 3-clause license]: LICENSE