Upload distribution when registering to PyPI

After registering a new version on PyPI, immediately upload the source
distribution package.
diff --git a/Makefile b/Makefile
index 31bf978..4adad1a 100644
--- a/Makefile
+++ b/Makefile
@@ -10,6 +10,7 @@
 
 register:
 	python setup.py register
+	python setup.py sdist upload
 
 site:
 	cd docs; make html