ksmbd: update documentation

configuration.txt in ksmbd-tools moved to ksmbd.conf manpage.
update it and more detailed ksmbd-tools build method.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Tom Talpey <tom@talpey.com>
Signed-off-by: Steve French <stfrench@microsoft.com>