CHANGELOG: update changelog-3.4

CHANGELOG-3.4.md

@@ -53,6 +53,7 @@ See [code changes](https://github.com/etcd-io/etcd/compare/v3.3.0...v3.4.0) and
 - Improve [index compaction blocking](https://github.com/etcd-io/etcd/pull/9511) by using a copy on write clone to avoid holding the lock for the traversal of the entire index.
 - Update [JWT methods](https://github.com/etcd-io/etcd/pull/9883) to allow for use of any supported signature method/algorithm.
 - Add [Lease checkpointing](https://github.com/etcd-io/etcd/pull/9924) to persist remaining TTLs to the consensus log periodically so that long lived leases progress toward expiry in the presence of leader elections and server restarts.
+  - Enabled by experimental flag "--experimental-enable-lease-checkpoint".
 - Add [gRPC interceptor for debugging logs](https://github.com/etcd-io/etcd/pull/9990); enable `etcd --debug` flag to see per-request debug information.
 - Add [consistency check in snapshot status](https://github.com/etcd-io/etcd/pull/10109). If consistency check on snapshot file fails, `snapshot status` returns `"snapshot file integrity check failed..."` error.
 - Add [`Verify` function to perform corruption check on WAL contents](https://github.com/etcd-io/etcd/pull/10603).