[GR-19691] Linux-aarch64 is supported since 21.2, not 20.2 (typo)

PullRequest: truffleruby/2846

Author: eregon

README.md

@@ -96,7 +96,7 @@ TruffleRuby is actively tested on the following systems:
 Architectures:
 
 * AMD64 (aka `x86_64`): Supported
-* AArch64 (aka `arm64`): Supported on Linux (from 20.2)
+* AArch64 (aka `arm64`): Supported on Linux (from 21.2)
 
 You may find that TruffleRuby will not work if you severely restrict the
 environment, for example, by unmounting system filesystems such as `/dev/shm`.