README: add maintainers section for hardware reference boards

Kevin Hao has stepped up to take care of issues specific to the meta-yocto-bsp
hardware reference boards. I'll also serve as a maintaier, so adding my name
as well.

To make this clear, let's add it to the README.hardware file that describes
the boards.

cc: Kevin Hao <kexin.hao@windriver.com>
(From meta-yocto rev: 7ea7fdf4a9ad0fcedf9a939e20146342d6ab1c57)

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

README.hardware

@@ -52,6 +52,13 @@ The following boards are supported by the meta-yocto-bsp layer:
 For more information see the board's section below. The appropriate MACHINE
 variable value corresponding to the board is given in brackets.
 
+Reference Board Maintenance
+===========================
+
+Send pull requests, patches, comments or questions about meta-yocto-bsps to poky@yoctoproject.org
+
+Maintainers: Kevin Hao <kexin.hao@windriver.com>
+             Bruce Ashfield <bruce.ashfield@windriver.com>
 
 Consumer Devices
 ================