Add coverage badge to README

.github/workflows/coverage-badge.yaml

@@ -0,0 +1,62 @@
+name: Coverage Badge
+
+on:
+  push:
+    branches: [ main ]
+    paths:
+      - 'llama_stack/**'
+      - 'tests/unit/**'
+      - 'uv.lock'
+      - 'pyproject.toml'
+      - 'requirements.txt'
+      - '.github/workflows/unit-tests.yml'
+      - '.github/workflows/codecov-badge.yaml' # This workflow
+  workflow_dispatch:
+
+jobs:
+  unit-tests:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python:
+          - "3.12"
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+
+      - name: Install dependencies
+        uses: ./.github/actions/setup-runner
+
+      - name: Run unit tests
+        run: |
+          PYTHON_VERSION=${{ matrix.python }} ./scripts/unit-tests.sh
+
+      - name: Coverage Badge
+        uses: tj-actions/coverage-badge-py@1788babcb24544eb5bbb6e0d374df5d1e54e670f # v2.0.4
+    
+      - name: Verify Changed files
+        uses: tj-actions/verify-changed-files@a1c6acee9df209257a246f2cc6ae8cb6581c1edf # v20.0.4
+        id: verify-changed-files
+        with:
+          files: coverage.svg
+
+      - name: Commit files
+        if: steps.verify-changed-files.outputs.files_changed == 'true'
+        run: |
+          git config --local user.email "github-actions[bot]@users.noreply.github.com"
+          git config --local user.name "github-actions[bot]"
+          git add coverage.svg
+          git commit -m "Updated coverage.svg"
+
+      - name: Create Pull Request
+        if: steps.verify-changed-files.outputs.files_changed == 'true'
+        uses: peter-evans/create-pull-request@271a8d0340265f705b14b6d32b9829c1cb33d45e # v7.0.8
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          title: "ci: [Automatic] Coverage Badge Update"
+          body: |
+            This PR updates the coverage badge based on the latest coverage report.
+
+            Automatically generated by the [workflow coverage-badge.yaml](.github/workflows/coverage-badge.yaml)
+          delete-branch: true