doc: note that signatures of binary may be from subkeys

PR-URL: #32591
Fixes: #32559
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>

README.md

@@ -548,7 +548,7 @@ maintaining the Node.js project.
 
 ### Release Keys
 
-GPG keys used to sign Node.js releases:
+Primary GPG keys for Node.js Releasers (some Releasers sign with subkeys):
 
 * **Beth Griggs** <bethany.griggs@uk.ibm.com>
 `4ED778F539E3634C779C87C6D7062848A1AB005C`