Add changelog for 0.5.0

Note the addition of withCredentials support.

@@ -136,6 +136,7 @@ bandwidth and viewport dimensions.
     - [Best RESOLUTION variant] OR [Best BANDWIDTH variant] OR [inital playlist in manifest]
 
 ## Release History
+ - 0.5.0: cookie-based content protection support (see `withCredentials`)
  - 0.4.0: Live stream support
  - 0.3.0: Performance fixes for high-bitrate streams
  - 0.2.0: Basic playback and adaptive bitrate selection