Update changelog (#4600)

* update changelog for snapshot format change

* Update CHANGELOG.md

Co-authored-by: steviez <steven@anza.xyz>

* cap

* pr

---------

Co-authored-by: steviez <steven@anza.xyz>

Author: HaoranYi

CHANGELOG.md

@@ -14,6 +14,9 @@ Release channels have their own copy of this changelog:
 
 <a name="edge-channel"></a>
 ## [2.2.0] - Unreleased
+* Breaking:
+  * Snapshot format change
+    * The snapshot format has been modified to implement SIMD-215. Since only adjacent versions are guaranteed to maintain snapshot compatibility, this means snapshots created with v2.2 are compatible with v2.1 and incompatible with v2.0 and older.
 * Changes
   * CLI:
     * Add global `--skip-preflight` option for skipping preflight checks on all transactions sent through RPC. This flag, along with `--use-rpc`, can improve success rate with program deployments using the public RPC nodes.