Update README.md

add notes about running multiple instances

examples/watchtower/README.md

@@ -1,3 +1,8 @@
 # References
 
 - https://github.com/containrrr/watchtower
+- https://containrrr.dev/watchtower/
+
+# Notes
+
+Running multiple Watchtower instances is only possible by using scope definitions. Please read [here](https://containrrr.dev/watchtower/running-multiple-instances/). Otherwise, any new Watchtower container will remove and clean up older instances.