Several small init script additions/improvements

- Added default file for init script to allow configuration for the runner
- Updated install area inside ReadMe.md
- Adapted the indention of the switch-case to match the rest of the script
- Renamed uppercase variables to lowercase vars
- Updated the check-if-Im-root-method to use the "new" EUID way
- Replaced `sudo` with `su -c`because on startup there is no tty where you can use `sudo`
- Edited the stop()-method to stop killing runners if there aren't any
- Remove PID-File when stopping