Add supermodeltools.com/trial CTA (#6)

* docs: add supermodeltools.com/trial CTA

* docs: punch up /trial CTA with 40%+ token-savings hook

Author: jonathanpopham

README.md

@@ -14,7 +14,9 @@ If this is useful, please star our tools — it helps us grow:
 
 ## Get an API key
 
-Get your API key from the [Supermodel Dashboard](https://dashboard.supermodeltools.com/) and send it in the `X-Api-Key` header.
+**Save 40%+ on agent token costs — start free → [supermodeltools.com/trial](https://supermodeltools.com/trial)**
+
+Send your API key in the `X-Api-Key` header.
 
 ## Quickstart