Add linting github action

.github/workflows/flake8.yaml

@@ -0,0 +1,17 @@
+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 flake8
+        run: flake8 cost-reporter/

README.md

@@ -1,6 +1,6 @@
 # Cost Reporter
 
-![Tests](https://github.com/globaldatanet/cost-reporter/workflows/Tests/badge.svg)
+![Tests](https://github.com/globaldatanet/cost-reporter/workflows/Tests/badge.svg) ![Linting](https://github.com/globaldatanet/cost-reporter/workflows/Linting/badge.svg)
 
 A lambda which sends a daily cost and trend report to slack. It helps with one of the three [**FinOps**](https://www.linkedin.com/company/finops-foundation/) phases: `Inform`. It can send you a report **every day** / **only when cost increases** / **only when cost breached a threshold** depending on your [configuration](template.yaml).