docs: Added documentation for native posix mode
docs: Added documentation for native posix mode

Added documentation for native posix mode.

Signed-off-by: Lingao Meng <d107961e9e4fef34975d9e927886461599dc7eda@xiaomi.com>

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Signed-off-by: Lingao Meng <d107961e9e4fef34975d9e927886461599dc7eda@xiaomi.com>

finikorg/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr