Try to setup CI.

.github/workflows/build_the_doc_test.yml

@@ -0,0 +1,23 @@
+---
+name: build_the_docs_test
+
+on:
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  btd:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - uses: buildthedocs/btd@67180e0ca49e3619f2475686946997cb4a478bc1
+        with:
+          token: ${{ github.token }}
+          skip-deploy: true
+
+      - uses: actions/upload-artifact@v2
+        with:
+          name: docs
+          path: docs/_build/html