docs: link shortener

Documentation.md

@@ -105,7 +105,23 @@ fullname = "Fullname"
 
 ## Link shortener for contacts
 
-<!-- TODO -->
+This file is stored at `/app/data/contacts/links.toml`
+
+```toml
+"a"   = "redirectiona.fr"
+"a/e" = "redirectiona.fr/something"
+"a/b" = "redirectiona.fr/amazing"
+"b"   = "other_site.com"
+```
+
+This is designed by a tuple (service \* optional-scope),
+separated by `/` -> `service/optional_scope`
+
+- links will be available at `/contact/service/scope` and `/c/service/scope`
+- the scope is optional
+- you can't stack up scope, only one scope is allowed
+
+> This is _by design_ to keep things easy
 
 # Add content