chore: add CHANGELOG entry for temporary removal of generic-simd support

Author: ytmimi

CHANGELOG.md

@@ -34,6 +34,7 @@
 - The unstable `required_version` configuration option now support semantic versioning [#6063](https://github.com/rust-lang/rustfmt/issues/6063)
 - Format `lazy_static::lazy_static!` like `lazy_static!` when setting `style_edition=2027` [#6287](https://github.com/rust-lang/rustfmt/issues/6287)
 - Top-level imports are no longer merged when setting `imports_granularity=Module`. Note that `imports_granularity=Module` is still an unstable configuration [#6191](https://github.com/rust-lang/rustfmt/issues/6191)
+- Disable the `bytecount/generic-simd` optional dependency when using the `generic-simd` feature. The dependency was preventing rustfmt from building on nightly. simd support will be re-enabled once the issue has been fixed [#6807](https://github.com/rust-lang/rustfmt/pull/6807) [llogiq/bytecount#100](https://github.com/llogiq/bytecount/pull/100)
 
 
 ### Added