Update index.bs

Co-authored-by: Domenic Denicola <[email protected]>

Author: youennf

index.bs

@@ -207,7 +207,7 @@ The <dfn>writeEncodedData</dfn> algorithm is given a |rtcObject| as parameter an
 
 A RTCRtpTransform has two private slots called `[[readable]]` and `[[writable]]`.
 
-On getting the transform attribute, the user agent MUST run the following steps:
+The <dfn attribute for="RTCRtpSender,RTCRtpReceiver">transform</dfn> getter steps are:
 1. Let |rtcObject| be the {{RTCRtpReceiver}} or {{RTCRtpSender}} on which the getter is invoked.
 2. Return |rtcObject|.`[[transform]]`.