message: Update help document address
diff: @@ -539,9 +539,9 @@ void SeafileTrayIcon::openHelp()
  {
  QString url;
  if (QLocale::system().name() == "zh_CN") {
  - url = "https://www.seafile.com/help/install/";
  + url = "https://cloud.seafile.com/published/seafile-user-manual/syncing_client/install_syncing_client.md";
  } else {
  - url = "https://www.seafile.com/en/help/install/";
  + url = "https://download.seafile.com/published/seafile-user-manual/syncing_client/install_sync.md";
  }
  QDesktopServices::openUrl(QUrl(url));
  