Update pkg/body-based-routing/README.md

Co-authored-by: Rob Scott <[email protected]>

Author: rramkumar1

pkg/body-based-routing/README.md

@@ -6,4 +6,9 @@ model name.
 As per OpenAI spec, it is standard for the model name to be included in the
 body of the HTTP request. However, most implementations do not support routing
 based on the request body. This extension helps bridge the gap for clients that
-are unable to write the model name into the headers themselves.
+This extension works by parsing the request body. If it finds a `model` parameter in the
+request body, it will copy the value of that parameter into a request header.
+
+This extension is intended to be paired with an `ext_proc` capable Gateway. There is not
+a standard way to represent this kind of extension in Gateway API yet, so we recommend
+referring to implementation-specific documentation for how to deploy this extension.