Enhancing Plugin Reference Documentation

[trueberryless]

The Plugin Reference Documentation gives a perfect overview of how to integrate with Starlight/ Astro by using hooks. However, especially the section addIntegration could be enhanced by adding further documentation for the following key points:

1. Install the integration on the consumer by defining the package as a peer dependency in your package.json of the plugin.
2. Furthermore it would be great to provide a link to peerDependencyMeta, if the peer dependency should be optional.
3. The code provided could be further improved to import react only after checking if it's not already installed on the consumer.

I want to mention and thank @ematipico and link to the original issue in the Astro repo.

[HiDeoo]

Pasting a few thoughts I shared on Discord to not forget them:

My first thought is that there is definitely room for improvements altho it could be tricky to get it right as it depends a lot on what the plugin is doing, we don't know if the plugin requires the integration to be a dep or a peer dep, if it's optional or not, etc. I assume we also don't want (and probably cannot) document peerDependenciesMeta (maybe it could be a link if we go that far).