doc: Mention Tor listening in release notes

Author: laanwj

doc/release-notes.md

@@ -151,6 +151,23 @@ mining with the getblocktemplate protocol to a pool: this will affect you at
 the pool operator's discretion, which must be no later than BIP65 achieving its
 951/1001 status.
 
+Automatically listen on Tor
+----------------------------
+
+Starting with Tor version 0.2.7.1 it is possible, through Tor's control socket
+API, to create and destroy 'ephemeral' hidden services programmatically.
+Bitcoin Core has been updated to make use of this.
+
+This means that if Tor is running (and proper authorization is available),
+Bitcoin Core automatically creates a hidden service to listen on, without
+manual configuration. This will positively affect the number of available
+.onion nodes.
+
+This new feature is enabled by default if Bitcoin Core is listening, and
+a connection to Tor can be made. It can be configured with the `-listenonion`,
+`-torcontrol` and `-torpassword` settings. To show verbose debugging
+information, pass `-debug=tor`.
+
 0.12.0 Change log
 =================