chore: add warning about outdatedness

Author: bitfl0wer

docs/protocols/chat.md

@@ -1,5 +1,16 @@
 # polyproto-chat Extension Specification
 
+:::danger
+
+This specification document is wildly **incomplete and outdated**! It needs to be (and will be) reworked and does not
+represent the current state of polyproto-chat.
+
+Please check out [the OpenAPI specification(s)](https://github.com/polyphony-chat/typespec-openapi/tree/main/build/3.1.0)
+of polyproto-chat instead, as they provide a much better overview of currently thought-of APIs and
+behaviors.
+
+:::
+
 **Namespace:** `chat`
 
 **Version:** `v1.0-alpha.1`