add mkdocs CI

.github/workflows/mkdocs.yml

@@ -0,0 +1,21 @@
+name: mkdocs
+on:
+  push:
+    branches:
+      - master
+permissions:
+  contents: write
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-python@v4
+        with:
+          python-version: 3.x
+      - uses: actions/cache@v2
+        with:
+          key: ${{ github.ref }}
+          path: .cache
+      - run: pip install -r user_guide/requirements.txt
+      - run: (cd user_guide ; mkdocs gh-deploy --force)