Add HistoryEditor.withNewBatch to docs (ianstormtaylor#5769)

Author: TyMick

docs/libraries/slate-history/history-editor.md

@@ -44,6 +44,12 @@ Undo to the previous saved state.
 Apply a series of changes inside a synchronous `fn`, These operations will
 be merged into the previous history.
 
+#### `HistoryEditor.withNewBatch(editor: HistoryEditor, fn: () => void): void`
+
+Apply a series of changes inside a synchronous `fn`, ensuring that the first
+operation starts a new batch in the history. Subsequent operations will be
+merged as usual.
+
 #### `HistoryEditor.withoutMerging(editor: HistoryEditor, fn: () => void): void`
 
 Apply a series of changes inside a synchronous `fn`, without merging any of