Add links to NumFOCUS to README. (#202)

Add links to NumFOCUS to README.

README.md

@@ -1,5 +1,6 @@
 # <img src="https://raw.githubusercontent.com/glotzerlab/signac/master/doc/images/logo.png" width="75" height="75"> signac - simple data management
 
+[![Affiliated with NumFOCUS](https://img.shields.io/badge/NumFOCUS-affiliated%20project-orange.svg?style=flat&colorA=E1523D&colorB=007D8A)](https://numfocus.org/sponsored-projects/affiliated-projects)
 [![PyPI](https://img.shields.io/pypi/v/signac.svg)](https://pypi.org/project/signac/)
 [![conda-forge](https://img.shields.io/conda/vn/conda-forge/signac.svg?style=flat)](https://anaconda.org/conda-forge/signac)
 ![CircleCI](https://img.shields.io/circleci/project/github/glotzerlab/signac/master.svg)
@@ -8,7 +9,6 @@
 [![PyPI-downloads](https://img.shields.io/pypi/dm/signac.svg?style=flat)](https://pypistats.org/packages/signac)
 [![Gitter](https://img.shields.io/gitter/room/signac/Lobby.svg?style=flat)](https://gitter.im/signac/Lobby)
 
-
 The [**signac** framework](https://signac.io) helps users manage and scale file-based workflows, facilitating data reuse, sharing, and reproducibility.
 
 It provides a simple and robust data model to create a well-defined indexable storage layout for data and metadata.
@@ -72,3 +72,5 @@ $ python -m unittest discover tests/
 When using **signac** as part of your work towards a publication, we would really appreciate that you acknowledge **signac** appropriately.
 We have prepared examples on how to do that [here](http://docs.signac.io/en/latest/acknowledge.html).
 **Thank you very much!**
+
+The signac framework is a [NumFOCUS Affiliated Project](https://numfocus.org/sponsored-projects/affiliated-projects).