docs[patch]: Add ls example selector link to how to index (#6588)

docs/core_docs/docs/how_to/index.mdx

@@ -62,6 +62,7 @@ These are the core building blocks you can use when building applications.
 - [How to: use example selectors](/docs/how_to/example_selectors)
 - [How to: select examples by length](/docs/how_to/example_selectors_length_based)
 - [How to: select examples by semantic similarity](/docs/how_to/example_selectors_similarity)
+- [How to: select examples from LangSmith few-shot datasets](/docs/how_to/example_selectors_langsmith)
 
 ### Chat models