Fbpcs: updated release notes for v2.6.0 B1322 (#2054)

Summary:
Pull Request resolved: #2054

We are going to promote B1322 to Canary. Adding change logs.

Reviewed By: joe1234wu

Differential Revision: D42592212

fbshipit-source-id: ae2603ea2aa9968516b735010e8c57760019de4b

fbpcs/CHANGELOG.md

@@ -13,7 +13,9 @@ Types of changes
 - `Security` in case This project adheres to
   [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased - 2.6.0] - put release date here
+## [Unreleased - 2.7.0] - put release date here
+
+## [2.6.0] - 2023-01-23
 ### Removed
 * Removed deprecated MPCInstanceRepository from fbpcs
 * Removed deprecated MPCService APIs after MPCInstance usaged been moved to StageStateInstance. (create/start/stop/get/update_instance)