zfsprops: add some guidance around choosing AES vs chapoly

Signed-off-by: Rob Norris <[email protected]>

man/man7/zfsprops.7

@@ -38,7 +38,7 @@
 .\" Copyright (c) 2019, Kjeld Schouten-Lebbing
 .\" Copyright (c) 2022 Hewlett Packard Enterprise Development LP.
 .\"
-.Dd April 18, 2023
+.Dd May 21, 2023
 .Dt ZFSPROPS 7
 .Os
 .
@@ -1096,6 +1096,12 @@ selected, which is currently
 In order to provide consistent data protection, encryption must be specified at
 dataset creation time and it cannot be changed afterwards.
 .Pp
+On systems lacking hardware-accelerated AES (many non-x86 boards)
+.Sy chacha20-poly1305
+will usually offer better performance without compromising security.
+On x86, or when datasets may be mounted on on older versions of ZFS, an AES
+suite is the best choice.
+.Pp
 For more details and caveats about encryption see the
 .Sx Encryption
 section of