Update the release process now that we have a setup.py file

CONTRIBUTING.md

@@ -11,6 +11,7 @@ testsuite with `python3 -m unittest discover -v` before submitting one :)
 
 1. Update the [changelog](https://0xacab.org/jvoisin/mat2/blob/master/CHANGELOG.md)
 2. Update the version in the [main.py](https://0xacab.org/jvoisin/mat2/blob/master/main.py) file
-3. Commit the changelog and the main.py file
-4. Create a tag with `git tag -s $VERSION`
-5. Push the tag with `git push --tags`
+3. Update the version in the [setup.py](https://0xacab.org/jvoisin/mat2/blob/master/setup.py) file
+4. Commit the changelog and the main.py file
+5. Create a tag with `git tag -s $VERSION`
+6. Push the tag with `git push --tags`