doc: update macOS specific guide for MacPorts
doc: update macOS specific guide for MacPorts

Add comment for the setup failure.
The solution can be infered from ARMmbed/cmsis-pack-manager#97
Fixes #18269.
Signed-off-by: Chen Guokai <3182814cd86329dbdd84e3c4cce6e7273929ff19@qq.com>

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