Add missing defineExpose import

[raulrpearson]

Description of Problem

An example on guide/essentials/template-refs.md is missing the import of defineExpose.

Proposed Solution

Add it.

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[skirtles-code]

Thanks for the PR, but defineExpose is a compiler macro and doesn't need to be imported.

[raulrpearson]

Interesting, I didn't know that. Do you think it would be worth mentioning that instead?

As a beginner I was a bit confused. I tested it out on a project and got a red squiggle under my use of defineExpose, so I assumed it required importing. I guess there's something wrong with my setup, then. (EDIT: ESLint is the one complaining in my case).

If you'd like me to suggest some phrasing for that "compiler macro" piece of information, let me know and I'll add a commit. Or feel free to add it yourself or close the PR if you think that's the best course of action. And thanks for the quick feedback!

[skirtles-code]

I've opened #2140 to try to address this. More work may be needed beyond that, as the concept of 'compiler macros' hasn't been introduced properly and we're largely glossing over it in that guide.