add detection for legacy browsers
It could be good to inform users if they are using a legacy browser and what to do about it.
related: https://forum.manjaro.org/t/erroneous-presentation-on-the-manjaro-website/86810/17
We can use this https://browser-update.org/, is easy to implement we can customise text and look, use their default page or build our own. @philm @oberon, what you think?