fix: cli oneliner for agents starter kit (#24523)

Author: threepointone

src/content/docs/agents/index.mdx

@@ -35,7 +35,7 @@ To use the Agent starter template and create your first Agent with the Agents SD
 
 ```sh
 # install it
-npm create cloudflare@latest agents-starter --template=cloudflare/agents-starter
+npm create cloudflare@latest agents-starter -- --template=cloudflare/agents-starter
 # and deploy it
 npx wrangler@latest deploy
 ```