Update update-a-batch-change.mdx (#894)

Added description of what happens to manually added commits when batch
change is updated

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docs/batch-changes/update-a-batch-change.mdx

@@ -60,6 +60,7 @@ Here are some examples:
 - When the [`changesetTemplate.title`](/batch-changes/batch-spec-yaml-reference#changesettemplatetitle) or the [`changesetTemplate.body`](/batch-changes/batch-spec-yaml-reference#changesettemplatecommitauthor) are changed and the changeset has been published, the changeset on the code host will be updated accordingly
 - When the [`changesetTemplate.branch`](/batch-changes/batch-spec-yaml-reference#changesettemplatetitle) is changed after the changeset has been published on the code host, the existing changeset will be closed on the code host and the new one, with the new branch, will be created
 - When the batch spec is changed in such a way that no diff is produced in a repository in which the batch change has already created and published a changeset, the existing changeset will be closed on the code host and archived in the batch change
+- When the changeset has been published and the batch spec is changed in such a way that a commit on the code host will be overwritten, any commits that have been manually added to the changeset on the code host will be deleted 
 
 <Callout type="note">See the [Batch Changes design](/batch-changes/design) docs for more information on the declarative nature of the Batch Changes system.</Callout>