Rollup merge of #142258 - teohhanhui:docs/platform-support-linux-kernel-version-or-later, r=workingjubilee

platform-support.md: Mention specific Linux kernel version or later

To be consistent with notes for other targets...

~~(Only made the change for `aarch64-unknown-linux-gnu` for now, as that's fairly certain after looking at the `git blame` just to be sure.)~~

Author: fmease