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

Author: teohhanhui

src/doc/rustc/src/platform-support.md

@@ -33,7 +33,7 @@ All tier 1 targets with host tools support the full standard library.
 target | notes
 -------|-------
 [`aarch64-apple-darwin`](platform-support/apple-darwin.md) | ARM64 macOS (11.0+, Big Sur+)
-`aarch64-unknown-linux-gnu` | ARM64 Linux (kernel 4.1, glibc 2.17+)
+`aarch64-unknown-linux-gnu` | ARM64 Linux (kernel 4.1+, glibc 2.17+)
 `i686-pc-windows-msvc` | 32-bit MSVC (Windows 10+, Windows Server 2016+, Pentium 4) [^x86_32-floats-return-ABI] [^win32-msvc-alignment]
 `i686-unknown-linux-gnu` | 32-bit Linux (kernel 3.2+, glibc 2.17+, Pentium 4) [^x86_32-floats-return-ABI]
 [`x86_64-apple-darwin`](platform-support/apple-darwin.md) | 64-bit macOS (10.12+, Sierra+)