upstream: mention that ed25519 is the default key type generated and

clarify that rsa-sha2-512 is the default signature scheme when RSA is in use.
Based on GHPR505 from SebastianRzk

OpenBSD-Commit-ID: 1d90df71636a04601685d2a10a8233bcc8d4f4c5

ssh-keygen.1

@@ -1,4 +1,4 @@
-.\"	$OpenBSD: ssh-keygen.1,v 1.232 2024/06/17 13:50:18 naddy Exp $
+.\"	$OpenBSD: ssh-keygen.1,v 1.233 2024/08/17 08:35:04 djm Exp $
 .\"
 .\" Author: Tatu Ylonen <[email protected]>
 .\" Copyright (c) 1995 Tatu Ylonen <[email protected]>, Espoo, Finland
@@ -35,7 +35,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: June 17 2024 $
+.Dd $Mdocdate: August 17 2024 $
 .Dt SSH-KEYGEN 1
 .Os
 .Sh NAME
@@ -581,7 +581,7 @@ Specifies the type of key to create.
 The possible values are
 .Dq ecdsa ,
 .Dq ecdsa-sk ,
-.Dq ed25519 ,
+.Dq ed25519 (the default),
 .Dq ed25519-sk ,
 or
 .Dq rsa .
@@ -594,7 +594,7 @@ The available RSA signature variants are
 .Dq rsa-sha2-256 ,
 and
 .Dq rsa-sha2-512
-(the default).
+(the default for RSA keys).
 .It Fl U
 When used in combination with
 .Fl s