DietPi Read-only filesystem question

Hi I am planning to use DietPi to run my home assistant installation. I would like to be able to set everything up, then make the entire sd card read only, so all writes will be made in RAM. I understand if the system reboots it will loose any changes. Is that what the read-only root filesystem option does? If I need to set up an overlay system, could someone explain how to do it? Thanks!