Add JOSS paper link & citation information to README
# Altair
[![build status](http://img.shields.io/travis/altair-viz/altair/master.svg?style=flat)](https://travis-ci.org/altair-viz/altair)
+[![JOSS Paper](http://joss.theoj.org/papers/10.21105/joss.01057/status.svg)](http://joss.theoj.org/papers/10.21105/joss.01057)
[![Binder](https://beta.mybinder.org/badge.svg)](https://beta.mybinder.org/v2/gh/altair-viz/altair_notebooks/master)
[![Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/altair-viz/altair_notebooks/blob/master/notebooks/Index.ipynb)
@@ -210,6 +211,11 @@ py.test --pyargs altair
See [`CONTRIBUTING.md`](https://github.com/altair-viz/altair/blob/master/CONTRIBUTING.md)
+## Citing Altair
+[![JOSS Paper](http://joss.theoj.org/papers/10.21105/joss.01057/status.svg)](http://joss.theoj.org/papers/10.21105/joss.01057)
+
+If you use Altair in an academic work, please consider citing http://joss.theoj.org/papers/10.21105/joss.01057
+
## Whence Altair?
Altair is the [brightest star](https://en.wikipedia.org/wiki/Altair) in the constellation Aquila, and along with Deneb and Vega forms the northern-hemisphere asterism known as the [Summer Triangle](https://en.wikipedia.org/wiki/Summer_Triangle).
