agents: Update prompts.mdx

Author: elithrar

src/content/docs/agents/build/prompts.mdx

@@ -13,6 +13,8 @@ When building, iterating on or debugging applications using AI tools and Large L
 
 We're providing an extensive example prompt that can help you build apps and AI agents using Cloudflare Workers and your preferred AI model.
 
+Use the click-to-copy button at the top right of the code block below to copy the full prompt to your clipboard:
+
 ```md collapse={30-10000}
 <system_context>
 You are an advanced assistant specialized in generating Cloudflare Workers code. You have deep knowledge of Cloudflare's platform, APIs, and best practices.