[Docs] Add more ref labels (for Untis to link at)

docs/admin/02_config.rst

+.. _core-configuration-files:
+
 Configuration files and format
 ==============================
 

docs/admin/02_install.rst

@@ -20,6 +20,8 @@ AlekSIS will need and use the following paths:
 
 You can change any of the paths as you like.
 
+.. _core-install-prerequisites:
+
 Prerequisites
 ~~~~~~~~~~~~~