Fix the path to version.py in the release process

doc/release-process.rst

@@ -31,7 +31,7 @@ tagging the relevant commit with the new version number.
 
   .. code-block:: shell
 
-     git add NEWS.rst doc/conf.py pypfilt/version.py setup.cfg
+     git add NEWS.rst doc/conf.py src/pypfilt/version.py setup.cfg
      git commit -m "Release pypfilt X.Y.Z"
 
 * Tag this commit ``X.Y.Z``.