improve vp8 description, thanks hta

Author: fippo

index.bs

@@ -452,8 +452,9 @@ interface RTCEncodedVideoFrame {
                         video/VP8
                     </td>
                     <td>
-                        The data is the "uncompressed data chunk" defined in
-                        [VP8](https://datatracker.ietf.org/doc/html/rfc6386#section-9.1).
+                        The data starts with the "uncompressed data chunk" defined in
+                        [VP8](https://datatracker.ietf.org/doc/html/rfc6386#section-9.1) and is followed
+                        by the rest of the frame data.
                         The [VP8 payload descriptor](https://www.rfc-editor.org/rfc/rfc7741#section-4.1)
                         is not accessible.
                     </td>