Add link to "Mixing Frameworks"

[JusticeMatthew]

I think we should add a link under the Mixing Frameworks heading that leads to Combining Multiple JSX Frameworks and a brief explainer

Something simple like:

"You can import and render components from multiple frameworks in the same Astro component. Additional configuration is required when mixing JSX frameworks"

• I am willing to submit a PR for this

[sarah11918]

Looks like a great place to me! Make it so! @JusticeMatthew - would take a PR, or an issue if you don't have the time!