Function add_comment 

pub fn add_comment(config: &Config, args: &[String]) -> Result<()>

Add a comment line to the logfile

Errors

• Return PathError::FilenameMissing if the log file has no filename.
• Return PathError::InvalidPath if the path part of log file is not a valid path.
• Return PathError::FileAccess if the log file cannot be opened or created.
• Return PathError::FileWrite if the function fails to append to the log file.