Update _config.yml

added extra footer with license information

Author: kthood

book/_config.yml

@@ -35,6 +35,10 @@ repository:
 html:
   use_issues_button: true
   use_repository_button: true
+  extra_footer: |
+    <p>
+    This work is licensed under a <a href="https://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</a>.
+    </p>
 
 #launch_buttons:
 #  notebook_interface        : "jupyterlab"