Preview pull requests

Closes gh-4.

.github/workflows/pages.yml

@@ -4,7 +4,7 @@ name: Deploy static content to Pages
 on:
   # Runs on pushes targeting the default branch
   push:
-    branches: ["main"]
+    branches: ["main", "gh-pages"]
 
   # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch:

.github/workflows/previews.yml

@@ -0,0 +1,22 @@
+name: Deploy PR previews
+
+on:
+  pull_request:
+    types:
+      - opened
+      - reopened
+      - synchronize
+      - closed
+
+concurrency: preview-${{ github.ref }}
+
+jobs:
+  deploy-preview:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Deploy preview
+        uses: rossjrw/pr-preview-action@v1
+        with:
+          source-dir: .