Extend the docs on setting the cipher list. Lutz Jaenicke <Lutz.Jaenicke@aet.TU-Cottbus.DE>

doc/ssl/SSL_CTX_set_cipher_list.pod

@@ -30,6 +30,15 @@ corresponding ciphers are not compiled in or because they are mistyped,
 are simply ignored. Failure is only flagged if no ciphers could be collected
 at all.
 
+It should be noted, that inclusion of a cipher to be used into the list is
+a necessary condition. On the client side, the inclusion into the list is
+also sufficient. On the server side, additional restrictions apply. All ciphers
+have additional requirements. ADH ciphers don't need a certificate, but
+DH-parameters must have been set. All other ciphers need a corresponding
+certificate and key. A RSA cipher can only be chosen, when a RSA certificate is
+available, the respective is valid for DSA ciphers. Ciphers using EDH need
+a certificate and key and DH-parameters.
+
 =head1 RETURN VALUES
 
 SSL_CTX_set_cipher_list() and SSL_set_cipher_list() return 1 if any cipher