Update README to include the ssh_keygen function

README

@@ -188,10 +188,20 @@ The following is a list of the currently available variables:
     included, like it is defined. So take care! Default: empty -> not added.
 
 
-Defines
--------
+Defines and functions
+---------------------
+
+Deploy authorized_keys file with the define sshd::ssh_authorized_key.
+
+Generate a public/private keypair with the ssh_keygen function. For example, the
+following will generate ssh keys and put the different parts of the key into
+variables:
+
+$ssh_keys = ssh_keygen("${$ssh_key_basepath}/backup/keys/${fqdn}/${backup_host}")
+$public_key = split($ssh_keys[1],' ')
+$sshkey_type => $public_key[0]
+$sshkey => $public_key[1]
 
-Deploy authorized_keys file with the define sshd::ssh_authorized_key
 
 Client
 ======