message: added explanation on how to submit PRs moving forward
diff: - [ ] By placing an `X` in the preceding checkbox, I verify that I have signed the [Contributor License Agreement](https://github.com/SeleniumHQ/selenium/blob/master/CONTRIBUTING.md#step-6-sign-the-cla)
  +
  +<!--
  +Selenium IDE is moving to an electron app!!!.
  +For the time being the team will support both the extension and the app, until the app reaches complete feature parity with the extension.
  +
  +If you want to submit a PR to the electron app, please submit to master.
  +To submit a PR to the extension submit to the branch v3
  +-->
  