Add default config files and improve README

Signed-off-by: kfei <kfei@kfei.net>
Create working directories if not presented

Also remove the user profiles volume, since the default setting is now
`/rtorrent/rutorrent/user-profiles`.

Signed-off-by: kfei <kfei@kfei.net>
Polish README

Signed-off-by: kfei <kfei@kfei.net>
Add .rtorrent.rc

Signed-off-by: kfei <kfei@kfei.net>