Fix link in summarization.md (#1344)

"Utilities for working with Documents" was linking to a non-useful page.
Re-linked to the utils page that includes info about working with docs.

docs/use_cases/summarization.md

@@ -15,6 +15,6 @@ The following resources exist:
 - [Summarization Notebook](../modules/indexes/chain_examples/summarize.ipynb): A notebook walking through how to accomplish this task.
 
 Additional related resources include:
-- [Utilities for working with Documents](../modules/utils/how_to_guides.rst): Guides on how to use several of the utilities which will prove helpful for this task, including Text Splitters (for splitting up long documents).
+- [Utilities for working with Documents](../reference/utils.rst): Guides on how to use several of the utilities which will prove helpful for this task, including Text Splitters (for splitting up long documents).
 - [CombineDocuments Chains](../modules/indexes/combine_docs.md): A conceptual overview of specific types of chains by which you can accomplish this task.
 - [Data Augmented Generation](./combine_docs.md): An overview of data augmented generation, which is the general concept of combining external data with LLMs (of which this is a subset).