docs: link CHANGELOG_OLD.md from README (repochecker S6020)

Completes the remaining piece of iobroker-bot PR #16; the CHANGELOG_OLD.md
file and all Node.js baseline/CI changes from PRs #14 and #15 are already
present in main.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: AlanSRU

README.md

@@ -137,6 +137,8 @@ Enable debug logging in the ioBroker admin to see detailed communication with th
 ### 0.3.2 (2026-03-24)
 * (Alan Paris) Improved telnet response parsing
 
+[Older changelogs can be found there](CHANGELOG_OLD.md)
+
 ## License
 
 MIT License