doc UPDATE add kbdint paragraph to the docs

doc/libnetconf.doc

@@ -391,11 +391,12 @@
  * Another option for authorized clients is to reference another endpoint's clients, however be careful not to create a cyclic reference
  * (see ::nc_server_config_add_ssh_endpoint_client_ref()). An authorized client MUST authenticate to all of it's configured authentication methods.
  *
- * The Keyboard Interactive authentication method is also supported. There are three options.
- * The first is to use Linux PAM. You need to specify the service name using ::nc_server_ssh_set_pam_conf_filename().
- * The second is to use the system's locally configured user's. The only Keyboard Interactive challenge will be the given
+ * \anchor ln2doc_kbdint
+ * The Keyboard Interactive authentication method is also supported. It can be done in three ways.
+ * If libpam is found, Linux PAM is used to handle the authentication. You need to specify the service name using ::nc_server_ssh_set_pam_conf_filename().
+ * Else if the standard functions for accessing local users are found on the system, they are used. The only Keyboard Interactive challenge will be the given
  * user's password (that is if he's found on the system).
- * The last option is to define your own callback to perform the authentication, see ::nc_server_ssh_set_interactive_auth_clb().
+ * Either way, you can always define your own callback to perform the authentication, see ::nc_server_ssh_set_interactive_auth_clb().
  * The callback has a higher priority than the other two methods.
  *
  * There are also some other optional settings.