code: function quitIfAlreadyRunning () {
    if (!electron.app.requestSingleInstanceLock()) {
      return electron.app.quit()
    }
    electron.app.on('second-instance', (event, commandLine, workingDirectory) => {
      // Someone tried to run a second instance, we should focus our window.
      if (windows.main) {
        if (windows.main.isMinimized()) windows.main.restore()
        windows.main.focus()
      }
    })
  }
docs: It's not possible to run two instances of patchwork as it would create two
  ssb-server instances that conflict on the same port. Before opening patchwork,
  we check if it's already running and if it is we focus the existing window
  rather than opening a new instance.