Show how to set license in guide's example

[edunham]

I hope that this will gently remind users that it's best practices to license
their code.

[rust-highfive]

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[steveklabnik]

So, I like this, but I also don't like the idea of picking a specific license in the example.

The other problem is that this doesn't work: Cargo doesn't generate this, which is how the tutorial works.

Maybe we can address this another way?

[alexcrichton]

I agree that choosing one would be nice to avoid, perhaps something like license = "..." and then a comment pointing where to get a list from?

[apasel422]

This could also incorporate a demonstration of #2013, if it's merged.

[alexcrichton]

I'm gonna close this for now (been inactive for awhile), but we'll likely revisit if #2013 is rebased/landed as part of the documentation!