README.md: Mention gorilla advantage re no extra context cancellation goroutine

Not sure how/when this was lost but an important disadvantage to note.

README.md

@@ -102,6 +102,8 @@ Advantages of [gorilla/websocket](https://github.com/gorilla/websocket):
 - Mature and widely used
 - [Prepared writes](https://pkg.go.dev/github.com/gorilla/websocket#PreparedMessage)
 - Configurable [buffer sizes](https://pkg.go.dev/github.com/gorilla/websocket#hdr-Buffers)
+- No extra goroutine per connection to support cancellation with context.Context. This costs nhooyr.io/websocket 2 KB of memory per connection.
+  - Will be removed soon with [context.AfterFunc](https://github.com/golang/go/issues/57928). See [#411](https://github.com/nhooyr/websocket/issues/411)
 
 Advantages of nhooyr.io/websocket: