docs: note imsg chats json

skills/imsg/SKILL.md

@@ -14,7 +14,7 @@ Requirements
 - Automation permission to control Messages.app (for sending)
 
 Common commands
-- List chats: `imsg chats --limit 10`
+- List chats: `imsg chats --limit 10 --json`
 - History: `imsg history --chat-id 1 --limit 20 --attachments --json`
 - Watch: `imsg watch --chat-id 1 --attachments`
 - Send: `imsg send --to "+14155551212" --text "hi" --file /path/pic.jpg`