Add docs GitHub Action

This is a temporary solution until we figure out how to
deploy readthedocs via GitHub Actions on a GitHub page.

.github/workflows/docs.yml

@@ -0,0 +1,18 @@
+name: "Docs"
+on: [push, pull_request]
+
+jobs:
+  docs:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: sphinx-toolbox/sphinx-action@master
+        with:
+          pre-build-command: "pip install .[docs]"
+          docs-folder: "docs/"
+      - name: Deploy
+        uses: peaceiris/actions-gh-pages@v3
+        if: github.ref == 'refs/heads/main'
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: docs/_build/html