Add GitHub Action to release to PyPI

[cooperlees]

• On a GitHub release creation Github actions will build + upload versions of xar

Addresses making releases happen so we don't get so stale again as reported in #43

[facebook-github-bot]

@cooperlees merged this pull request in facebookincubator/xar@ed011cb9d02af16f5f2184310659008783ae222b.