add changelog for #7255

Author: tsnobip

CHANGELOG.md

@@ -30,6 +30,7 @@
 - AST cleanup: remove "|." and rename "|." to "->" in the internal representation for the pipe operator. https://github.com/rescript-lang/rescript/pull/7244
 - AST cleanup: represent concatenation (`++`) and (dis)equality operators (`==`, `===`, `!=`, `!==`) just like in the syntax. https://github.com/rescript-lang/rescript/pull/7248
 - AST cleanup: use inline record for `Ptyp_arrow`. https://github.com/rescript-lang/rescript/pull/7250
+- Playground: Bundle stdlib runtime so that the playground can execute functions from Core/Belt/Js. (#7255)
 
 # 12.0.0-alpha.7