Display a warning on outdated UAs

[thcrt]

It could be frustrating for users of extremely outdated browsers (IE, old versions of Chrome/Safari/FF) to see a site styled in potentially unexpected and unintended ways. I have no interest in supporting these browsers, and in fact actively think we should not ever support them. But it could be a good idea to implement some kind of warning on users that send UserAgent strings indicating an outdated browser.

[vinay-nb]

Hye @thcrt I would like to work on this, I will set up project locally and let you know

[thcrt]

@vinay-nb sounds good! welcome to the team :)