Add 'yarn schema' command to CONTRIBUTING.md

[binste]

No description provided.

[domoritz]

Thanks for the pull request. I think we should rebuild the schema on build instead. What do you think?

[binste]

Sounds good, I'd find that more convenient. To only compile VL without the schema one can still use build:only. I adjusted package.json (tested the command) and reverted the change in CONTRIBUTING.md.

yarn build is used in .github/workflows/test.yml and .release-it.json. I'm not familiar enough with the package to know if it's ok if the schema is now also rebuilt in those places.

[domoritz]

Yeah, we need to comprehensively look through the scripts. I don't have time right now but will look at some point to resolve the issue you found.