ci: add GitHub actions to build docs site

.github/workflows/docs.yml

@@ -0,0 +1,51 @@
+name: Deploy docs
+
+on:
+  push:
+    branches: [master]
+  workflow_dispatch:
+
+# Sets permissions of the GITHUB_TOKEN to allow deployment to GitHub Pages
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+# Allow one concurrent deployment
+concurrency:
+  group: "pages"
+  cancel-in-progress: true
+
+jobs:
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@main
+
+      - name: Setup Magic Nix cache
+        uses: DeterminateSystems/magic-nix-cache-action@main
+
+      - name: Install dependencies
+        run: nix develop ./nix --impure --command bash -c "cd docs && npm install"
+
+      - name: Build
+        run: nix develop ./nix --impure --command bash -c "cd docs && npm run build"
+
+      - name: Setup Pages
+        uses: actions/configure-pages@v3
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v2
+        with:
+          path: docs/build
+
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v2