Added sftp_enabled, sftp_chroot_dir, and ssh_client_roaming from the defaults

Sftp is disabled by default. Some people might miss this at a glance.
Some ansible module will not work without sftp, so `scp_if_ssh = True` needs to
be set in ansible.cfg.
Currently there's a bug in ansible 2.0.1.0 that ignores the parameter.

#55

Author: KuroKatze

README.md

@@ -36,7 +36,9 @@ This role provides secure ssh-client and ssh-server configurations.
 * ``ssh_allow_groups: ''`` - if specified, login is allowed only for users whose primary group or supplementary group list matches one of the patterns.
 * ``ssh_print_motd`` - false to disable printing of the MOTD
 * ``ssh_print_last_log`` - false to disable display of last login information
-
+* ``sftp_enabled`` - true to enable sftp configuration
+* ``sftp_chroot_dir`` - change default sftp chroot location
+* ``ssh_client_roaming`` - enable experimental client roaming
 
 ## Example Playbook