Add release git tag

[melund]

@tisimst Thank you for an extremely useful library. I am creating a conda recipe to build it for conda-forge: https://github.com/conda-forge

Would you consider adding tag for the newest version on github. Just add a git tag with the string 0.3.8. That would make it simpler to refer to a specific version on github, and simplify the recipe a bit.

You can see the proposed recipe here: conda-forge/staged-recipes#1046

[melund]

So. We ended up linking to the pypi source instead. I would rather point directly to the GitHub release, but this will do for now. So there is no rush here.

PyDOE is now on conda forge. See https://github.com/conda-forge/pydoe-feedstock

So with conda, installing is as easy as:

> conda config --add channels conda-forge
> conda install pydoe

@tisimst I will happily add you as maintainer/admin as well. Otherwise, I will just keep it updated.