[nrf fromtree] samples: boards: nordic: clock_control: add README.rst#3633

bjarki-andreasen wants to merge 1 commit intonrfconnect:mainnrfconnect/sdk-zephyr:mainfrom

bjarki-andreasen:samples-boards-nordic-clock-control-docbjarki-andreasen/sdk-zephyr:samples-boards-nordic-clock-control-docCopy head branch name to clipboard