add instruction for github workflow

Author: AntSimi

.github/workflows/python-app.yml

@@ -25,6 +25,9 @@ jobs:
         python -m pip install --upgrade pip
         pip install flake8 pytest
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+    - name: Install package
+      run: |
+        pip install -e .
     - name: Lint with flake8
       run: |
         # stop the build if there are Python syntax errors or undefined names