fix PR number in changelog

Author: elfkuzco

CHANGELOG.md

@@ -7,7 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- Set up documentation using `mkdocs`, published on readthedocs.com (#186)
+- Set up documentation using `mkdocs`, published on readthedocs.com (#215)
 
 ## [3.6.0] - 2024-10-15