docs: fix open agent skills section not rendering in README

Add a blank line between the closing </details> tag and the
"Installing using open agent skills tool" heading so GitHub parses
it as a heading, and add the missing step 1 label for consistency.

Author: twishabansal

README.md

@@ -228,10 +228,13 @@ Enter your environment vars as described in the [configuration section](#configu
 _(Tip: Run `codex plugin list` or use the `/plugins` interactive menu to verify your installed plugins.)_
 
 </details>
+
 ## Installing using [open agent skills tool](https://github.com/vercel-labs/skills)
 
 You can install skills using the `npx skills` command.
 
+**1. Install the skills:**
+
 Run the following command in your terminal to automatically download and register the skills:
 
 ```bash