chore: add back the comment

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

lib/Service/Install/SignSetupService.php

@@ -534,6 +534,7 @@ private function createSignatureData(array $hashes): array {
 		$privateKey = $this->getPrivateKey();
 		$privateKey->withPadding(RSA::SIGNATURE_PSS);
 		$privateKey->withMGFHash('sha512');
+		// See https://tools.ietf.org/html/rfc3447#page-38
 		$privateKey->withSaltLength(0);
 		$signature = $privateKey->sign(json_encode($hashes));