[workers] add Changing Usage Models subheading

Author: rohinlohe

src/content/docs/workers/platform/pricing.mdx

@@ -99,10 +99,14 @@ If you had a Worker on the Bundled usage model prior to the migration to Standar
 
 :::
 
+### How to switch usage models
+
 :::note
 
 Some Workers Enterprise customers maintain the ability to change usage models.
 
+:::
+
 Usage models may be changed at the individual Worker level:
 
 1. Log in to the [Cloudflare dashboard](https://dash.cloudflare.com) and select your account.