Update ref.md

[runleonarun]

What are you changing in this pull request and why?

Adding that you need to set cross project dependencies when using 2 arguments with projects. Per feedback from @b-per 🙇🏻

Checklist

• Review the Content style guide and About versioning so my content adheres to these guidelines.
• Add a checklist item for anything that needs to happen before this PR is merged, such as "needs technical review" or "change base branch."

Adding new pages (delete if not applicable):

• Add page to website/sidebars.js
• Provide a unique filename for the new page

Removing or renaming existing pages (delete if not applicable):

• Remove page from website/sidebars.js
• Add an entry website/static/_redirects
• Ran link testing to update the links that point to the deleted page

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