Fix deployment issue and re-release 1.6.3

A long_description is required for the project to be published, the
README.rst is used for this. Tested with twine check.

Author: pgjones

pyproject.toml

@@ -4,6 +4,7 @@ license = {file = "LICENSE.rst"}
 authors = [{name = "Jason Kirtland", email = "[email protected]"}]
 maintainers = [{name = "Pallets Ecosystem", email = "[email protected]"}]
 description = "Fast, simple object-to-object and broadcast signaling"
+readme = "README.rst"
 keywords = [
     "signal",
     "emit",