Add a changelog entry for a recent feature (#406)

Note the change to add a `pattern` argument to the NumberFormat constructors.

PiperOrigin-RevId: 378049926
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 615d9f2..3f2542a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,7 @@
 ## 0.17.1-dev
 
+* Add optional parameter to `NumberFormat.compact()` to provide custom pattern.
+
 ## 0.17.0
  * Migrate to null safety.
  * Add `@pragma('vm:prefer-inline')` to `Intl` methods that already have