README - User has to be in docker group to build

[ehsjoar]

The README.md file suggests "NOTE: To run the commands without sudo, add your username to the Docker group using the following command: $ sudo usermod -aG docker ${USER}"

The fact is that you cannot run "make all" without being in the docker group or you have to have sudo powers. We need to update the README.md file so that adding the user that will build ODIM to the docker group is not optional.