Update README to clarify /skills add is a CLI prompt command

- Add numbered steps for adding the skill
- Emphasize that command must be typed at the > prompt
- Warn users not to paste it as a conversation message
- Add note explaining /skills add is a built-in CLI command

Fixes confusion between CLI prompt commands and chat messages

Co-authored-by: DUBSOpenHub <158339470+DUBSOpenHub@users.noreply.github.com>

Author: Copilot

README.md

@@ -32,12 +32,15 @@ Designed for **absolute beginners**. Even if you've never touched a terminal, we
 
 ### Add the Skill
 
-Inside a Copilot CLI session, run:
+1. Open a Copilot CLI session (run `copilot` in your terminal)
+2. At the `>` prompt, **type** the following slash command (do not paste it into a conversation):
 
 ```
 /skills add DUBSOpenHub/copilot-cli-quickstart
 ```
 
+> **Note:** `/skills add` is a built-in CLI command — it must be entered directly at the prompt, not sent as a chat message.
+
 That's it! One command. You're ready. 🎉
 
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