Add UDP Tracker specification to References section

README.rst

@@ -482,6 +482,8 @@ References
 * `BitTorrent: Extension for Peers to Send Metadata Files <http://www.bittorrent.org/beps/bep_0009.html>`_
 * `BitTorrent: Extension Protocol <http://www.bittorrent.org/beps/bep_0010.html>`_
 * `BitTorrent: Multitracker Metadata Extension <http://www.bittorrent.org/beps/bep_0012.html>`_
+* `BitTorrent: UDP Tracker Protocol for BitTorrent <http://www.bittorrent.org/beps/bep_0015.html>`_
+  and `BitTorrent udp-tracker protocol specification <http://www.rasterbar.com/products/libtorrent/udp_tracker_protocol.html>`_.
 * `BitTorrent: WebSeed - HTTP/FTP Seeding (GetRight style) <http://www.bittorrent.org/beps/bep_0019.html>`_
 * `BitTorrent: Private Torrents <http://www.bittorrent.org/beps/bep_0027.html>`_
 * `BitTorrent: BitTorrent DHT Extensions for IPv6 <http://www.bittorrent.org/beps/bep_0032.html>`_