Improve NewGoroutine doc.
@@ -306,6 +306,8 @@ func (txn *Transaction) BrowserTimingHeader() *BrowserTimingHeader {
//
// All Transaction methods can be used in any Transaction reference.
// The Transaction will end when End() is called in any goroutine.
+// Note that any segments that end after the transaction ends will not
+// be reported.
//
// Example passing a new Transaction reference directly to another
// goroutine:
