Fix cli example to use input argument in the right position.

[joarfish]

Fix #31

[happenslol]

Which platform have you tested this on? Seems to be more of a question concerning clap, but I don't remember it working this way... I'm going to look into it soon

[joarfish]

I tested it on windows 10 and macos.
I could not find anything explicit about this in clap's documentation. However, the way sheep uses clap it seems the input files have to be specified before the options.