Update README.md

Author: aaronkaplan

README.md

@@ -11,7 +11,7 @@ The IEPs should be discussion on the [intelmq-dev Mailinglist](https://lists.cer
 |001|[Configuration Handling](001/)|[Implementation completed](https://github.com/certtools/intelmq/projects/9)|3.0.0|
 |002|[Mixins](002/)|[Implementation completed](https://github.com/certtools/intelmq/projects/10)|3.0.0|
 |003|[Internal Data Format: Multiple Values](003/)|Dismissed|3.0.0|
-|004|[Internal Data Format: Meta Information and Data Exchange](004/)|Decided and formalized via JSON Schema|3.x.0 or 4.0.0|
+|004|[Internal Data Format: Meta Information and Data Exchange](004/)|Decided and formalized via a [JSON Schema](004/schema/schema.json)|3.x.0 or 4.0.0|
 |005|[Internal Data Format: Notification settings](005/)|Undiscussed|3.x.0 or 4.0.0|
 |006|[Internal Data Format: Msgpack as serializer](006/)|Undiscussed|3.x.0 or 4.0.0|