Compile using 'make' as a test for PRs

.github/workflows/pr.yml

@@ -0,0 +1,15 @@
+name: CI
+on:
+  pull_request:
+    branches:
+      - main
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Test build before merge
+        uses: actions/checkout@v2
+
+      - name: Test build
+        run: |
+          make