docs: update warning about using yarn

[chrisbrainerd]

Old warning was out of date - updated with something friendlier and more current. Fixes #3784

[welcome]

💖 Thanks for opening this pull request! 💖

Here is a list of things that will help get it across the finish line:

• Run yarn lint locally to catch formatting errors. This will fix some errors automatically, commit and push any changes.
• Run yarn test locally to catch errors. This ensures all components still behave as they should.
• Run yarn start to run the doc site locally and try a few pages, ensuring everything is in good working order.
• Include tests when adding/changing behavior.

We get a lot of pull requests on this repo, so please be patient and we will get back to you as soon as we can.

[azalisa]

Found this PR because I am affected by issue #3784, but I think you may have linked to it by mistake? The issue that seems to me like the best fit for this PR is issue #3815.

[chrisbrainerd]

Yupppp - thank you 🙃
I was also thinking of looking at that one and had the tab open, sorry about that!

[levithomason]

👍 !

[welcome]

Congrats on merging your first pull request! 🎉🎉🎉

[charliematters]

I raised #3784, and I suspect that this PR doesn't fix it? #3784 has been marked as closed now though - do you mind if I reopen it?

[charliematters]

@levithomason So I can't re-open it and I don't want to add a duplicate issue. Can you re-open it please?