Feature: Option to include warning message in compiled CSS file

[sselfridge]

Version: 1.13.0

Is the issue reproducible after updating to the latest version ( npm update less-watch-compiler)? Yes

Recently started working on a project using this and had never used less before. Started changing the .css file for styling changes because we didn't know better.

Would be helpful to have a commented message at the top of the CSS file:

// this is an auto-generated file by less-watch-compiler. This will be overwritten