fixed error description for observers that throw errors

src/Utils.js

@@ -52,7 +52,7 @@ module.exports = function (Y /* : any*/) {
         try {
           this.eventListeners[i](event)
         } catch (e) {
-          console.error('User events must not throw Errors!')
+          console.error('Your observer threw an error. This error was caught so that Yjs still can ensure data consistency! In order to debug this error you have to check "Pause On Caught Exceptions"', e)
         }
       }
     }