Add more descriptions about the script exit codes

[mathbalduino]

Is your feature request related to a problem? Please describe.
Currently, I couldn't find information about when the script exits with error (exit code != 0) or not

Describe the solution you'd like
It would be nice to have a concise way of knowing when the script will exit with an error or not. Currently, I've added it to my crontab and I wanted to run other commands in case of failure/success. I'm not sure what will happen, because I'm not sure about the exit codes, so I'll need to take a look into it in the next few months

Describe alternatives you've considered
Just add it to the README of the project. You can answer this issue and I can open a PR, no problem

Thanks!