Add some information to CSS files

[mRizvandi]

Prerequisites

• I have searched for duplicate or closed feature requests
• I have read the contributing guidelines

Proposal

Hi

I use these icons for long time and have a problem with file version published on website!
There is not any information as comment on the css files, when we download it from website.
We have to add date and version to downloaded files to our project to control the last update of icons.
Please add some License and Version information on css files.

Thanks.

• License - Fixed by font: add license header #1636
• Version

Motivation and context

Version control when we want to use the css files

[XhmikosR]

License will be fixed by #1636. As for the version, maybe later, because we'll need to automate it.