refactor: ♻️ point to guidebook for contributing in footer (#131)

# Description

Closes #127

No review needed.

Author: lwjohnst86

_extensions/seedcase-theme/_extension.yml

@@ -38,7 +38,7 @@ contributes:
           - text: "Code of Conduct"
             href: "https://github.com/seedcase-project/.github/blob/main/CODE_OF_CONDUCT.md"
           - text: "Contributing"
-            href: "https://community.seedcase-project.org/guides/"
+            href: "https://guidebook.seedcase-project.org/"
           - text: "Funded by the Novo Nordisk Foundation"
             href: https://seedcase-project.org/#acknowledgements