docs: add changelog and contributing files (#23)

Author: lwasser

CHANGELOG.md

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+# Changelog 
+

CONTRIBUTING.md

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+# Contributing to the pyos-sphinx theme
+
+We use nox to build our sphinx theme. For instructions on
+getting started with a local development workflow, see our
+[development page](https://www.pyopensci.org/pyos-sphinx-theme/develop.html).

README.md

@@ -1,14 +1,27 @@
 # ``pyos-sphinx-theme``
+
 [![Documentation Status](https://readthedocs.org/projects/pyos-sphinx-theme/badge/?version=latest)](https://pyos-sphinx-theme.readthedocs.io/en/latest/?badge=latest)
 [![PyPI version](https://badge.fury.io/py/pyos-sphinx-theme.svg)](https://badge.fury.io/py/pyos-sphinx-theme)
 <!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
 [![All Contributors](https://img.shields.io/badge/all_contributors-3-orange.svg?style=flat-square)](#contributors-)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
 
-A modified version of the [PyData Sphinx Theme](github.com/pydata/sphinx-theme) for use with the [pyOpenSci](https://pyopensci.org) project.
+[![All Contributors](https://img.shields.io/github/all-contributors/pyOpenSci/pyos-sphinx-theme?color=ee8449)](#contributors-)
+
+A modified version of the [PyData Sphinx Theme](github.com/pydata/sphinx-theme) that is used to keep the [pyOpenSci](https://pyopensci.org) organization repo books visually in sync.
 
 ## Contributors
 
 Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/docs/en/emoji-key)):
 
+<!-- ALL-CONTRIBUTORS-LIST:START - Do not remove or modify this section -->
+<!-- prettier-ignore-start -->
+<!-- markdownlint-disable -->
+
+
+<!-- markdownlint-restore -->
+<!-- prettier-ignore-end -->
+
+<!-- ALL-CONTRIBUTORS-LIST:END -->
+
 This project follows the [all-contributors](https://github.com/all-contributors/all-contributors) specification. Contributions of any kind welcome!