Update the README with a Code of Conduct badge (#1873)

README.md

@@ -1,6 +1,6 @@
 # Betty 👵
 
-![Test status](https://github.com/bartfeenstra/betty/workflows/Test/badge.svg?branch=0.3.x) [![Code coverage](https://codecov.io/gh/bartfeenstra/betty/branch/0.3.x/graph/badge.svg)](https://codecov.io/gh/bartfeenstra/betty) [![PyPI releases](https://badge.fury.io/py/betty.svg)](https://pypi.org/project/betty/) [![Supported Python versions](https://img.shields.io/pypi/pyversions/betty.svg?logo=python&logoColor=FBE072)](https://pypi.org/project/betty/) [![Recent downloads](https://img.shields.io/pypi/dm/betty.svg)](https://pypi.org/project/betty/) [![Follow Betty on Twitter](https://img.shields.io/twitter/follow/Betty_Project.svg?label=Betty_Project&style=flat&logo=twitter&logoColor=4FADFF)](https://twitter.com/Betty_Project)
+![Test status](https://github.com/bartfeenstra/betty/workflows/Test/badge.svg?branch=0.3.x) [![Code coverage](https://codecov.io/gh/bartfeenstra/betty/branch/0.3.x/graph/badge.svg)](https://codecov.io/gh/bartfeenstra/betty) [![PyPI releases](https://badge.fury.io/py/betty.svg)](https://pypi.org/project/betty/) [![Supported Python versions](https://img.shields.io/pypi/pyversions/betty.svg?logo=python&logoColor=FBE072)](https://pypi.org/project/betty/) [![Recent downloads](https://img.shields.io/pypi/dm/betty.svg)](https://pypi.org/project/betty/) [![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.1-4baaaa.svg)](CODE_OF_CONDUCT.md) [![Follow Betty on Twitter](https://img.shields.io/twitter/follow/Betty_Project.svg?label=Betty_Project&style=flat&logo=twitter&logoColor=4FADFF)](https://twitter.com/Betty_Project)
 
 Betty visualizes and publishes your family history by building interactive, encyclopedia-like genealogy websites out of your
 [Gramps](https://gramps-project.org/) and [GEDCOM](https://en.wikipedia.org/wiki/GEDCOM) family trees.