Add the details of the GitHub repository

Add the details of the GitHub repository of the JSON Schema project.

Author: benjagm

topics/json-schema/index.md

@@ -8,6 +8,7 @@ short_description: JSON Schema is a vocabulary that allows you to validate, anno
   documents.
 topic: json-schema
 url: https://json-schema.org/
+github_url: https://github.com/json-schema-org
 related: json
 ---
 While JSON is probably the most popular format for exchanging data, **JSON Schema** is the vocabulary that enables JSON data consistency, validity, and interoperability at scale.