Add changelog entry for #309

Author: lookback-hugotunius

media/CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Breaking
 
 * Introduced a new field in `Sample`, `prev_padding_packets`, that reflects the number of observed padding only packets while building the Sample. This can be use to differentiate inconsequential padding packets being dropped from those carrying media. Contributed by [@k0nserv](https://github.com/k0nserv) in [#303](https://github.com/webrtc-rs/webrtc/pull/303).
+* Improve handling of padding packets in `SampleBuiler`. Prior to this `SampleBuilder` would sometimes, incorrectly, drop packets that carry media when they appeared adjacent to runs of padding packets. Contributed by [@k0nserv](https://github.com/k0nserv) in [#309](https://github.com/webrtc-rs/webrtc/pull/309)
 
 ## v0.4.7