Improve documentation clarity for namespace option

Clarify that namespace is used for internal redirects and provide a concrete
example showing when and how to use it when the forward path differs from
the desired UI path structure.

Author: camilohollanda

lib/fun_with_flags/ui/router.ex

@@ -4,16 +4,17 @@ defmodule FunWithFlags.UI.Router do
 
   ## Options
 
-  * `:namespace` - The namespace to mount the UI under (default: `""`)
+  * `:namespace` - Path prefix for internal redirects. Use when the UI is mounted
+    under a sub-path that differs from the forward path (default: `""`)
   * `:disable_csrf` - Disable CSRF protection when the host application
     provides its own CSRF protection (default: `false`)
 
   ## Usage
 
-      # Basic usage
+      # Basic usage - UI available at /feature-flags/flags, /feature-flags/new, etc.
       forward "/feature-flags", FunWithFlags.UI.Router
 
-      # With namespace
+      # With namespace - forward at /admin but UI redirects go to /admin/feature-flags/*
       forward "/admin", FunWithFlags.UI.Router, namespace: "feature-flags"
 
       # Disable CSRF when host app provides protection