Example documentation for adding new boot-source-selection is missing positional argument

[Diogo Matsubara]

See http://maas.ubuntu.com/docs/bootsources.html#adding-a-source, the example after "
Inside that newly created source (‘2’) you can add selections:" says

$ maas $PROFILE boot-source-selections create os="ubuntu" release="trusty" arches="amd64" subarches="*" labels='*'

when it should be:
$ maas $PROFILE boot-source-selections create 2 os="ubuntu" release="trusty" arches="amd64" subarches="*" labels='*'

If you try to execute the example you'll get an not so user friendly error like:

invalid literal for int() with base 10: 'os=ubuntu'