Compile and render Synapse's docs into a browsable, mobile-friendly and searchable website (#10086)

.github/workflows/docs.yaml

@@ -0,0 +1,31 @@
+name: Deploy the documentation
+
+on:
+  push:
+    branches:
+      - develop
+
+  workflow_dispatch:
+
+jobs:
+  pages:
+    name: GitHub Pages
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Setup mdbook
+        uses: peaceiris/actions-mdbook@4b5ef36b314c2599664ca107bb8c02412548d79d # v1.1.14
+        with:
+          mdbook-version: '0.4.9'
+
+      - name: Build the documentation
+        run: mdbook build
+
+      - name: Deploy latest documentation
+        uses: peaceiris/actions-gh-pages@068dc23d9710f1ba62e86896f84735d869951305 # v3.8.0
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          keep_files: true
+          publish_dir: ./book
+          destination_dir: ./develop