readme: add link to rendered version

and remove mention of webcodecs

Author: fippo

README.md

@@ -2,10 +2,9 @@
 
 This repository contains a **proposal** for an API that allows the
 insertion of user-defined processing steps in the pipeline that
-handles media in a WebRTC context.
+handles encoded media in a WebRTC context.
 
 In order to allow such processing, it defines a number of extensions
-to the objects defined in [WEBRTC-PC](https://w3c.github.io/webrtc-pc/) and
-draws upon definitions from [WEBRTC-CODEC](https://github.com/WICG/web-codecs).
-
+to the objects defined in [WEBRTC-PC](https://w3c.github.io/webrtc-pc/).
 
+The editors' work-in-progress version of the document is at https://w3c.github.io/webrtc-encoded-transform/