add linter

.github/workflows/main.yml

@@ -18,6 +18,10 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           pip install -r requirements.txt
+      - name: Lint code with flake8
+        run: |
+          pip install flake8
+          flake8
 
       # TODO: it would be nice to have the project published on Pypi for easy installation via pip:
       #- name: Publish package