doc: relnotes: add notes about MISRA-C
doc: relnotes: add notes about MISRA-C

Update release notes with MISRA-C info.

Signed-off-by: Flavio Ceolin <979b9165500b0741b9d0500e2efd74fc1547bff7@intel.com>

nashif/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,ldts/zephyr,galak/zephyr,Vudentz/zephyr,finikorg/zephyr,ldts/zephyr,Vudentz/zephyr,ldts/zephyr,ldts/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,nashif/zephyr