UI: In SSH key creation page, list supported key types (only RSA right now)

templates/key/new.hamlet

@@ -12,7 +12,13 @@ $# You should have received a copy of the CC0 Public Domain Dedication along
 $# with this software. If not, see
 $# <http://creativecommons.org/publicdomain/zero/1.0/>.
 
-Enter the details and click "Submit" to add a new SSH key.
+<p>
+  Enter the details and click "Submit" to add a new SSH key.
+
+<p>
+  Currently, the only supported key type is RSA (i.e. public keys that start
+  with the "ssh-rsa"). Ed25519 support is planned; if you'd like that, open a
+  ticket or tell me about it, to make it a higher priority :)
 
 <form method=POST action=@{KeysR} enctype=#{enctype}>
   ^{widget}