docs: add setup-python to example (#27)

README.md

@@ -23,12 +23,13 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+      - uses: aws-actions/setup-sam@v0
       - uses: aws-actions/configure-aws-credentials@v1
         with:
           aws-access-key-id: ${{ secrets.AWS_ACCESS_KEY_ID }}
           aws-secret-access-key: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
           aws-region: us-east-2
-      - uses: aws-actions/setup-sam@v0
       # Build inside Docker containers
       - run: sam build --use-container
       # Prevent prompts and failure when the stack is unchanged