Add link to build instructions in README

[2400030303]

Editorial: Add build instructions reference to README

This PR adds a direct link to the build instructions in CONTRIBUTING.md, helping new contributors preview changes locally more easily.

This addresses the concern raised in:
Fixes #11867

No behavioral, testing, or implementation changes.

[sideshowbarker]

Suggested change

	We appreciate all contributions, see the [guidelines for contributing](CONTRIBUTING.md) for details, including information on how to build HTML output from the `source` file so you can preview your changes locally.
	To preview changes locally, see the build instructions in CONTRIBUTING.md:
	https://github.com/whatwg/html/blob/main/CONTRIBUTING.md#building-the-standard
	We appreciate all contributions. See the [guidelines for contributing](CONTRIBUTING.md) for details, including information on [how to build HTML output](https://github.com/whatwg/html/blob/main/CONTRIBUTING.md#building-the-standard) from the `source` file, so you can preview your changes locally.

[sideshowbarker]

You’ll need to sign the WHATWG Participation Agreement. See https://participate.whatwg.org/agreement-status?user=2400030303&repo=html&pull=11868

[annevk]

As-is this change appears to be incorrect. And with the suggested change applied it's still incorrect.

Given that we've had the existing setup in place for a long time I'm a little hesitant to make the README more verbose on the basis of a single complaint.

[sideshowbarker]

I'm a little hesitant to make the README more verbose on the basis of a single complaint.

Not sure it’s even a complaint — I mean, given the PR author is the same person who reported the issue it asserts to fix. And that the PR was raised less than 10 minutes after that issue was reported.

As-is this change appears to be incorrect. And with the suggested change applied it's still incorrect.

OK then yeah — given that in combination with the above, I change my vote to “close without merging”.