added readme for multisite

Author: Schmaetz

cluster-tutorials/multisite/Readme.md

@@ -0,0 +1,12 @@
+# Important note on the multisite cluster
+
+The cluster manifest alone is not sufficient to set up a multisite cluster correctly. Additional configuration steps are required, which are described in the documentation.
+
+**Please consult the complete documentation at the following URL before proceeding with the setup:**
+
+[Multisite cluster documentation](https://cybertec-postgresql.github.io/CYBERTEC-pg-operator/multisite/)
+
+> Without considering the further configuration steps, malfunctions or unexpected behaviour may occur in the cluster.
+
+## Further information
+For questions or support, please contact the responsible team or consult the official documentation.