Add Zenodo DOI

[eschnett]

Zenodo offers DOIs for released packages. See e.g. the DOI badge at https://github.com/eschnett/FastArrays.jl for an example.

It would be good if this package had an example for this. DOIs help make software citable.

Creating such DOIs is straightforward. Essentially, one adds the repo to Zenodo as one would for Travis or Appveyor https://zenodo.org/account/settings/github/, and Zenodo then tracks all releases made on Github and creates DOIs.

[samusz]

I don't see any DOI on Julia's repo.

Shouldn't it be more urgent than the Example.jl repo ?