Add Github workflow

.github/workflows/ci.yml

@@ -0,0 +1,16 @@
+name: CI
+on:
+  workflow_dispatch:
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: nixbuild/nix-quick-install-action@v9
+        with:
+          nix_version: 2.4
+          nix_conf: experimental-features = nix-command flakes
+      - name: nix build
+        run: nix -L build .#