Summary: This PR add the `space-evenly` prop, to the [justify-content.md](https://github.com/facebook/yoga/blob/master/website/contents/properties/justify-content.md) file. The description was taken from [Mozilla](https://developer.mozilla.org/en-US/docs/Web/CSS/justify-content) Pull Request resolved: https://github.com/facebook/yoga/pull/918 Differential Revision: D16701547 Pulled By: davidaurelio fbshipit-source-id: cd1bb7dd20cb1184a1bafb0d8f33e851051bd9e5