MAINT: enable custom URL

Author: mmcky

.github/workflows/publish.yml

@@ -87,7 +87,7 @@ jobs:
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: _build/html/
-          # cname: intro.quantecon.org
+          cname: intro.quantecon.org
       - name: Upload "_build" folder (cache)
         uses: actions/upload-artifact@v2
         with: