add building docs

Author: hpk42

.github/workflows/docs.yaml

@@ -0,0 +1,23 @@
+name: documentation
+
+on:
+  pull_request:
+  push:
+
+jobs:
+  scripts:
+    name: deploy-chatmail tests 
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: initenv 
+        run: scripts/initenv.sh
+
+      - name: build documentation 
+        working-directory: doc
+        run: venv/bin/sphinx-build source build
+
+      - name: build documentation second time (for TOC)
+        working-directory: doc
+        run: venv/bin/sphinx-build source build