github: add build and publish workflow

.github/workflows/build-site.yml

@@ -0,0 +1,46 @@
+name: build-site
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v20
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+      - name: Build Sprokkel
+        run: nix build .#sprokkel
+
+      - name: Build site
+        run: ./result/bin/sprokkel build ./example/sprokkel.uint.one
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: ./out
+
+  deploy:
+    runs-on: ubuntu-latest
+    needs: build
+
+    permissions:
+      pages: write
+      id-token: write
+
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+
+    steps:
+      - name: Deploy site
+        id: deployment
+        uses: actions/deploy-pages@v4