add GitHub workflow for building and running tests

.github/workflows/build-and-test.yml

@@ -0,0 +1,12 @@
+name: Build and run tests
+
+on: [pull_request, push]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Build
+        run: make test