Update README.md

Author: mfranzke

README.md

@@ -4,7 +4,7 @@ SPDX-FileCopyrightText: 2025 DB Systel GmbH
 SPDX-License-Identifier: Apache-2.0
 -->
 
-# db-ux-design-system.github.io
+# db-ux-design-system.github.io (with custom domain design-system.deutschebahn.com)
 
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