Add note on xpop gen timeout

lib/onTransaction.mjs

@@ -59,6 +59,10 @@ const onTransaction = async ({
                   })
                 )
               }, 500)
+              //  ^^ To check: is this enough? If e.g. retrieving the ledger info
+              //     would take longer this may not be enough. Best solution:
+              //     make this await the ledger fetching calls.
+              //     Dirty: extend to e.g. 2000.
             }
           })
         }