Update CHANGELOG.md

Co-authored-by: Sebastian <sebix@sebix.at>

Author: kamil-certat

CHANGELOG.md

@@ -19,7 +19,7 @@
 
 ### Data Format
 
-- added `severity` field to help with triaging received events (PR# by Kamil Mańkowski).
+- added `severity` field to help with triaging received events (PR#2575 by Kamil Mańkowski).
   To allow saving the field in PostgreSQL database in existing installations, the following schema update is necessary: `ALTER TABLE events ADD severity varchar(10);`.
 
 ### Bots