Incorrect link to PWA documentation in serviceWorker.js

[SeanReece]

In serviceWorker.js the link in the comments inviting the user to learn more about PWA seems to be broken.

// To learn more about the benefits of this model and instructions on how to
// opt-in, read http://bit.ly/CRA-PWA

http://bit.ly/CRA-PWA points to templates/README.md#making-a-progressive-web-app (anchor doesn't exist) when it should (I think) point to facebook.github.io/create-react-app/docs/making-a-progressive-web-app

I don't mind submitting a PR to fix this but I'm assuming that it would be wiser to update the bitlink itself so any links outside this repo will also point to the correct documentation.

Thanks!

[iansu]

Unfortunately bit.ly won't allow us to change those links. I've created a PR to add placeholders in the template README that provide links to the corresponding pages in the docs: #5808