Update README.md

Add a guide for using in repo mode

README.md

@@ -86,6 +86,43 @@ jobs:
 
 You can find a more in-depth example here: https://github.com/aquasecurity/trivy-sarif-demo/blob/master/.github/workflows/scan.yml
 
+### Using Trivy to scan your Git repo
+It's also possible to scan your git repos with Trivy's built-in repo scan. If you have [GitHub code scanning](https://docs.github.com/en/github/finding-security-vulnerabilities-and-errors-in-your-code/about-code-scanning) available you can use Trivy as a scanning tool as follows:
+```yaml
+name: build
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-18.04
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Build an image from Dockerfile
+        run: |
+          docker build -t docker.io/my-organization/my-app:${{ github.sha }} .
+
+      - name: Run Trivy vulnerability scanner in repo mode
+        uses: aquasecurity/trivy-action@master
+        with:
+          scan-type: 'fs'
+          ignore-unfixed: true
+          format: 'template'
+          template: '@/contrib/sarif.tpl'
+          output: 'trivy-results.sarif'
+          severity: 'CRITICAL'
+
+      - name: Upload Trivy scan results to GitHub Security tab
+        uses: github/codeql-action/upload-sarif@v1
+        with:
+          sarif_file: 'trivy-results.sarif'
+```
+
 ## Customizing
 
 ### inputs