Updated release steps in README.

The `build` module doesn't create the `build` folder in the local directory.
It's probably also worth cleaning up the .egg-info in the last step.

README.rst

@@ -146,7 +146,7 @@ Then, build and push the packages::
 
     python -m build
     twine upload dist/*
-    rm -r build/ dist/
+    rm -r asgiref.egg-info dist
 
 
 Implementation Details