Update the Starlark changelog

Summary: There are 650 commits, and I don't think anyone has time to produce a great changelog. Kinda sucks, but better a release than not, so hey ho.

Reviewed By: IanChilds

Differential Revision: D67192294

fbshipit-source-id: 13f5220713ed2e763919a0335b42f84c5d85d7ea

Author: ndmitchell

CHANGELOG.md

@@ -1,5 +1,15 @@
 # Starlark
 
+## 0.13 (Dec 13, 2024)
+
+- Some API changes (but alas, too many for us to enumerate).
+- Move to more Python-like type annotations, e.g. `dict[str, int]` now.
+- Support for the `set` data type.
+- Improve documentation, both the docs and the doc generator.
+- Performance improvements.
+- More trait implementation (`Trace`, `Allocative`, `AllocValue` etc).
+- Bump dependencies.
+
 ## 0.12 (Feb 9, 2024)
 
 - Implemented `reverse()` for `SmallMap`.