Update changelog

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+* **Breaking**: Snake case normalization (ex. function names) now correctly segments numbers.
+  For example, an operation `v2example` is now output as `v2_example`.
+  This may be a breaking change for clients with numbers in operation IDs.
+
 * **Add**: New configuration option `naming.field_casing` to choose between `:camel` case, `:snake` case, or performing no normalization (`nil`, the default).
   Using this option may be necessary for API descriptions that include non-normalized field names (for example, fields that begin with a number or symbol).
   Setting this configuration would be a breaking change for any clients based on API descriptions that have inconsistent field casing.