Link to pre-1.0 changelog

Author: babolivier

CHANGES.md

@@ -6440,3 +6440,5 @@ Internal Changes
 - Various improvements to debug logging. ([\#5353](https://github.com/matrix-org/synapse/issues/5353))
 - Don't run CI build checks until sample config check has passed. ([\#5370](https://github.com/matrix-org/synapse/issues/5370))
 - Automatically retry buildkite builds (max twice) when an agent is lost. ([\#5380](https://github.com/matrix-org/synapse/issues/5380))
+
+**Changelogs for versions older than 1.0.0 can be found [here](CHANGES-pre-1.0.md)