[README Docs Request] A remark on setup-ros vs Docker already setup

[SteveMacenski]

After chatting with @emersonknapp about why some used configurations don't have the

      - uses: ros-tooling/setup-ros@v0.7
        with:
          required-ros-distributions: humble

stage, he mentioned that it's not necessary if using the rostooling based docker images with setup-ros done already which speeds up CI. I'd suggest adding a clear remark about that in the readme since that is a pretty ideal setup to use by default (unless users know better) so that their CI jobs are much, much faster without having to setup all of ROS.

[elad-eyal]

hopefully a full example with the name of a docker image which can be used for that

[elad-eyal]

I tried the simplest example from the README on GitHub actions. After 6h of installing ROS it canceled my job; I guess if I had a container ready it would be faster.