improved comments

network/message/sendE2E.go

@@ -69,6 +69,9 @@ func (m *Manager) SendE2E(msg message.Send, param params.E2E) ([]id.Round, error
 		}(i)
 	}
 
+	// while waiting check if any rekeys need to happen and trigger them. This
+	// can happen now because the key popping happens in this thread,
+	// only the sending is parallelized
 	keyExchange.CheckKeyExchanges(m.Context, partner)
 
 	wg.Wait()