Add Code of Conduct badge

Author: Relequestual

README.md

@@ -1,5 +1,5 @@
 # Welcome to JSON Schema
-[![Financial Contributors on Open Collective](https://opencollective.com/json-schema/all/badge.svg?label=financial+contributors)](https://opencollective.com/json-schema)
+[![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.1-4baaaa.svg)](https://github.com/json-schema-org/.github/blob/main/CODE_OF_CONDUCT.md) [![Financial Contributors on Open Collective](https://opencollective.com/json-schema/all/badge.svg?label=financial+contributors)](https://opencollective.com/json-schema)
 
 JSON Schema is a vocabulary that allows you to validate, annotate, and manipulate JSON documents.