doc: add macOS arm64 experimental status

PR-URL: #40127 Reviewed-By: Richard Lau <rlau@redhat.com>

Author: mrienstra

BUILDING.md

@@ -114,6 +114,7 @@ platforms. This is true regardless of entries in the table below.
 | Windows | x64, x86 | Windows Server 2012 (not R2) | Experimental | |
 | Windows | arm64 | >= Windows 10 | Tier 2 (compiling) / Experimental (running) | |
 | macOS | x64 | >= 10.11 | Tier 1 | |
+| macOS | arm64 | >= 11 | Experimental | |
 | SmartOS | x64 | >= 18 | Tier 2 | |
 | AIX | ppc64be >=power7 | >= 7.2 TL02 | Tier 2 | |
 | FreeBSD | x64 | >= 11 | Experimental | Downgraded as of Node.js 12 <sup>[7](#fn7)</sup> |