Add linting github action

.github/workflows/flake8.yaml

@@ -0,0 +1,18 @@
+name: Linting
+
+on: [push]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Setup Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.8
+      - name: Install Flake8
+        run: pip install flake8
+      - name: Run Tox
+        # Run tox using the version of Python in `PATH`
+        run: flake8 cost-reporter/