corrected outdated link (#15053)

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libs/community/langchain_community/document_loaders/markdown.py

@@ -24,7 +24,7 @@ class UnstructuredMarkdownLoader(UnstructuredFileLoader):
 
     References
     ----------
-    https://unstructured-io.github.io/unstructured/bricks.html#partition-md
+    https://unstructured-io.github.io/unstructured/core/partition.html#partition-md
     """
 
     def _get_elements(self) -> List: