readme: Add information about the TF-A IRC channel
readme: Add information about the TF-A IRC channel

Fixes ARM-software/tf-issues#607

Change-Id: I5637f53e7f4857c85ee8b3af06ebcf86b9e4f1bc
Signed-off-by: Dimitris Papastamos <5172875e934a989df22d22726b6d9d921b91fbdd@arm.com>

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware