Updated changelog

Changelog.rst

@@ -10,6 +10,7 @@ Changes
 * Added ``alias`` optional parameter to ``SSHClient`` and ``HostConfig`` for passing through from parallel clients.
   Used to set an SSH host name alias, for cases where the real host name is the same and there is a need to
   differentiate output from otherwise identical host names - #355. Thank you @simonfelding.
+* Parallel clients now read a common private key only once, reusing it for all ``SSHClient``s to improve performance.
 * Performance improvements for all clients when reading output.
 * Output reading for all clients has been changed to be less prone to race conditions.