Add 2023.10 update changelog

Changelog.md

@@ -1,3 +1,9 @@
+## 2023.10 Update
+1. A series of additional security checks in node: special cells in action list, init state in external messages, peers data prior to saving to disk.
+2. Human-readable timestamps in explorer
+
+Besides the work of the core team, this update is based on the efforts of @akifoq and @mr-tron.
+
 ## 2023.06 Update
 1. (disabled by default) New deflation mechanisms: partial fee burning and blackhole address
 2. Storage-contract improvement