docs: clarify Lab and Lch round trips

[xianjianlf2]

Fixes #295

Summary

• document that Lab/Lch round trips should keep the same Lab white point
• call out Chroma.js default D65 white point and D50 differences in other tools
• point users to chroma.setLabWhitePoint(...) when matching another conversion tool

Validation

• git diff --check
• Not run: test suite (docs only).

[changeset-bot]

⚠️ No Changeset found

Latest commit: a43c2a9

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR