scripts/dts: Document Bindings._include()
scripts/dts: Document Bindings._include()

Explain that it implements !include.

Signed-off-by: Ulf Magnusson <01743f1c1deb1fe75271d62edb65757d98ac0bcb@nordicsemi.no>

explora26/zephyr,ldts/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,nashif/zephyr,ldts/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,nashif/zephyr,galak/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,Vudentz/zephyr,explora26/zephyr,galak/zephyr,ldts/zephyr,nashif/zephyr,Vudentz/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr