docs: add webauthn_id changes to CHANGELOG

Author: santiagorodriguez96

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Changed
 
+- Change `webauthn_id` generation from `after_initialize` to `before_validation` and add a data backfill to the `webauthn_id` migration generator for existing records. [@santiagorodriguez96]
 - Options for getting or creating passkeys and security keys are now served by dedicated Rails controllers and retrieved via JavaScript fetch requests. [#73](https://github.com/cedarcode/devise-webauthn/pull/73) [@nicolastemciuc]
 - BREAKING!: Remove helpers for generating WebAuthn options. [#106](https://github.com/cedarcode/devise-webauthn/pull/115) [@nicolastemciuc]