add binder button

pg_cs/_config.yml

@@ -25,7 +25,7 @@ repository:
   use_issues_button: true
   use_repository_button: true
 
-#launch_buttons:
+launch_buttons:
   notebook_interface: "classic" # or  "jupyterlab"
   binderhub_url: "https://notebooks.gesis.org/binder/"
 #  colab_url: "https://colab.research.google.com"