fix broken links due to missing site_url on mkdocs.yml

mkdocs.yml

@@ -18,6 +18,7 @@
 site_name: UNICADO                        # The name of the site, displayed in the header.
 repo_url: https://git.rwth-aachen.de/unicado/unicado-package  # Link to the Git repository, will appear in the header.
 repo_name: UNICADO Repository             # Name for the Git repository link in the header.
+site_url: "https://unicado.pages.rwth-aachen.de/unicado.gitlab.io/" # The actual site url -> IMPORTANT: site-urls relies on this (site: will be replaced directly)!
 
 # === Site configuration ===
 markdown_extensions: