📝(CHANGELOG) added PR id to changelog

Author: PedroManse

CHANGELOG.md

@@ -10,7 +10,7 @@ and this project adheres to
 
 ## Added
 
-- ♿️(nix) Added nix environment declaration
+- ♿️(nix) Added nix environment declaration #751
 - ✨(frontend) add pinning on doc detail #711
 - 🚩(frontend) feature flag analytic on copy as html #649
 - ✨(frontend) Custom block divider with export #698