add workflow

.github/workflows/build.yaml

@@ -0,0 +1,17 @@
+name: Build project
+
+on:
+  pull_request:
+  push:
+  workflow_dispatch:
+
+jobs:
+  main:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@main
+
+      - name: Build
+        run: nix build "github:$GITHUB_REPOSITORY/$GITHUB_SHA" -L