Add GitHub Actions (#1193)

.github/workflows/test.yml

@@ -0,0 +1,23 @@
+name: "Run tests"
+
+on:
+  - push
+  - pull_request
+
+env:
+  FORMAT_FILE: README.md
+
+jobs:
+  test:
+    name: 'Validate README.md'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: Validate Markdown format
+        run: build/validate_format.py ${FORMAT_FILE}
+
+      - name: Validate pull request changes
+        run: build/github-pull.sh ${{ github.repository }} ${{ github.event.pull_request.number }} ${FORMAT_FILE}
+        if: github.event_name == 'pull_request'