docs: add entry for added code snippets in aggregator (#4809)

# Motivation

Add an entry in SNS Aggregator changelog about the code snippets that
have been added in PR
[#4086](#4086).

# Changes

- add text `Add common code snippets for developers to the
"Documentation" chapter on the landing page.`

CHANGELOG-Sns_Aggregator.md

@@ -11,6 +11,7 @@ The SNS Aggregator is released through proposals in the Network Nervous System.
 ### Added
 
 - Include SNS nervous system parameters.
+- Add common code snippets for developers to the "Documentation" chapter on the landing page.
 
 ### Changed
 ### Deprecated