docs: Mention Open IoT SDK limitations

- Document the latest supported version for the
SDK (v2022.07). Versions of the Open IoT SDK above
the version currently referenced are not
supported.

- Document known issue of CMSIS-FreeRTOS invalid
tag referenced in the current used version of
Open IoT SDK.

Signed-off-by: Ahmed.Ismail <Ahmed.Ismail@arm.com>