Update config ptr (#207)

Author: jorgensd

_config.yml

@@ -21,7 +21,7 @@ execute:
 repository:
   url: https://github.com/jorgensd/dolfinx-tutorial # Online location of your book
   path_to_book: . # Optional path to your book, relative to the repository root
-  branch: main # Which branch of the repository should be used when creating links (optional)
+  branch: release # Which branch of the repository should be used when creating links (optional)
 
   # Add a bibtex file so that we can create citations
 bibtex_bibfiles: