Add CI to build and test on Linux

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

@@ -0,0 +1,21 @@
+name: Build and test on Linux
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build_and_test:
+
+    runs-on: ubuntu-20.04
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Build
+      run: make
+
+    - name: Test
+      run: make test