Add a bit more help text to client:only description

[JusticeMatthew]

📚 Subject area/topic

client-directives

📋 Suggested page

https://github.com/withastro/docs/blob/main/src/content/docs/en/reference/directives-reference.mdx

📋 General description or bullet points (if proposing new content)

I would like to add some additional text to the client:only directive to inform the user of why you would use it versus client:load which is more performant.

I've seen the question come up a few times in the discord and I think a single sentence along the lines of Use this directive if your components need access to browser-specific APIs or to resolve hydration mismatch errors from framework components

🖥️ Reproduction of code samples in StackBlitz

No response