📝 Document options in the README

Author: webknjaz

README.md

@@ -3,6 +3,15 @@
 A GitHub Action to unpack a source distribution package (tarball / `.tar.gz`) into the current workspace
 
 
+## Options
+
+This action only has two inputs — `source-tarball-name` (default:
+`*.tar.gz`) and `workflow-artifact-name` (default:
+`python-package-distributions`). It downloads the latter and works with
+the sdist matching the former glob to make its contents available in the
+current working directory.
+
+
 ## Any users?
 
 At the moment, it is used by the [@CherryPy] upstream, more to come.