readme: Add support for RD-N1-Edge platform in readme.rst

FVP_RD_N1Edge is the Fixed Virtual Platform on which the
Trusted Firmware-A Tests are executed for RD-N1-Edge

Change-Id: If6ffaa5430b9d41caf6d0697896bc92114e9a87c
Signed-off-by: Chandni Cherukuri <chandni.cherukuri@arm.com>
1 file changed