Box UI Elements installation page doesn't properly list the maximum React version (the <19 part)

The documentation regarding installation off [UI Elements](content/guides/embed/ui-elements/installation.md) doesn't list the maximum React version (<19).

Since React 19 has been in stable release since 2024-12-05 ([source](https://react.dev/blog/2024/12/05/react-19)), it's important to let users know they may need to downgrade React to use this the npm package for this library (until that's no longer the case).

I believe a few small copy edits on the page I referenced above would be enough to alert users to the situation although there may be other pages that repeat the same info (and thus would need similar changes).