readme: Add information about the TF-A IRC channel

Fixes ARM-software/tf-issues#607

Change-Id: I5637f53e7f4857c85ee8b3af06ebcf86b9e4f1bc
Signed-off-by: Dimitris Papastamos <dimitris.papastamos@arm.com>

readme.rst

@@ -219,6 +219,13 @@ See the `Contributing Guidelines`_ for information on how to contribute to this
 project and the `Acknowledgments`_ file for a list of contributors to the
 project.
 
+IRC channel
+~~~~~~~~~~~
+
+Development discussion takes place on the #trusted-firmware-a channel
+on the Freenode IRC network. This is not an official support channel.
+If you have an issue to raise, please use the `GitHub issue tracker`_.
+
 Feedback and support
 ~~~~~~~~~~~~~~~~~~~~