Add Binder link

Author: brian-rose

_config.yml

@@ -21,9 +21,12 @@ bibtex_bibfiles:
 
 # Information about where the book exists on the web
 repository:
-  url: https://projectpythia.github.io/pythia-foundations  # Online location of your book
+  url: https://github.com/ProjectPythia/pythia-foundations  # Online location of your book
   #path_to_book: docs  # Optional path to your book, relative to the repository root
   branch: main  # Which branch of the repository should be used when creating links (optional)
+# Configure your Binder links, such as the URL of the BinderHub.
+launch_buttons:
+  binderhub_url             : https://mybinder.org
 
 # Add GitHub buttons to your book
 # See https://jupyterbook.org/customize/config.html#add-a-link-to-your-repository