Completion for `rfkill`

Written myself.
Is `nfc` not needed?

```
$ rfkill
Usage:	rfkill [options] command
Options:
	--version	show version (0.5-1ubuntu1 (Ubuntu))
Commands:
	help
	event
	list [IDENTIFIER]
	block IDENTIFIER
	unblock IDENTIFIER
where IDENTIFIER is the index no. of an rfkill switch or one of:
	<idx> all wifi wlan bluetooth uwb ultrawideband wimax wwan gps fm nfc
[14-08-26.18:23]vagrant@vagrant-ubuntu-trusty-64: ~
$ rfkill --version
rfkill 0.5-1ubuntu1 (Ubuntu)
```