README.hardware.md: add genericarm64 maintainers

Add maintainers section to genericarm64 machine documentation.

(From meta-yocto rev: d7ee71aea43873bf2d28b6b7cb15900242659440)

Signed-off-by: Mikko Rapeli <mikko.rapeli@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-yocto-bsp/README.hardware.md

@@ -145,6 +145,8 @@ building the image also build the `u-boot` recipe to build the required
 firmware (note that this firmware will _not_ boot on real hardware), then use
 `runqemu` as usual.
 
+Maintainers:
+* Ross Burton <Ross.Burton@arm.com>
 
 Texas Instruments Beaglebone (beaglebone-yocto)
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