Document how to preview changes locally

Yesterday in https://chat.mozilla.org/#/room/#mdn:mozilla.org @Elchi3 shared how to preview changes of BCD locally. I've tried it out locally and it boils down to this:

Check out https://github.com/mdn/browser-compat-data, https://github.com/mdn/content and https://github.com/mdn/yari in the same directory. Then:

cd path/to/yari
yarn add link:../browser-compat-data
echo CONTENT_ROOT=../content/files > .env
yarn dev

Then find a page that includes the BCD table you've changed, which in my case is http://localhost:3000/en-US/docs/Web/API/DOMPoint#browser_compatibility.

Changes to BCD require stopping and starting the server.

Documenting this for all contributors would be nice. Even nicer would be wrapping it into something like npm run preview which would generate a page with any modified tables and open that. It would be a small step from there to providing preview as part of the CI system.

Start by reviewing the existing preview workflow across the browser-compat-data, content, and yari repositories, using the listed yarn commands and localhost page as the entry point. Document the local BCD preview steps for contributors, including the need to restart the server after BCD changes; any preview command or CI extension is a broader follow-up.