Mention the IRC channels used for discussions about ARM/ARM64
sub-architectures and Devicetree.  This documents purely existing state.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20220207175503.425200-2-krzysztof.kozlowski@canonical.com

'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>