chore: Add info about changes that override upstream values

Signed-off-by: Roman Nikitenko <rnikiten@redhat.com>

Author: RomanNikitenko

.rebase/CHANGELOG.md

@@ -2,6 +2,12 @@
 
 The file to keep a list of changed files which will potentionaly help to resolve rebase conflicts.
 
+#### @RomanNikitenko
+https://github.com/che-incubator/che-code/pull/539
+
+- code/src/vs/platform/extensionManagement/common/abstractExtensionManagementService.ts
+---
+
 #### @RomanNikitenko
 https://github.com/che-incubator/che-code/pull/557