Update README.md

Author: ringabout

README.md

@@ -2,7 +2,7 @@
 HTTP Cookies for Nim.
 This module provides the `Cookie` type, which directly maps to Set-Cookie HTTP response headers, and the `CookieJar` type which contains many cookies.
 
-Overview
+## Overview
 `Cookie` type is used to generate Set-Cookie HTTP response headers. Server sends Set-Cookie HTTP response headers to the user agent. So the user agent can send them back to the server later.
 
 `CookieJar` contains many cookies from the user agent.