Add defunct disclaimer to dataset card

README.md

@@ -78,6 +78,10 @@ dataset_info:
 
 ### Dataset Summary
 
+<div class="course-tip course-tip-orange bg-gradient-to-br dark:bg-gradient-to-r before:border-orange-500 dark:before:border-orange-800 from-orange-50 dark:from-gray-900 to-white dark:to-gray-950 border border-orange-50 text-orange-700 dark:text-gray-400">
+  <p><b>Defunct:</b> Dataset "the_pile_stack_exchange" is defunct and no longer accessible due to unavailability of the source data.</p>
+</div>
+
 This dataset is part of EleutherAI/The Pile dataset and is a dataset for Language Models from processing stackexchange data dump, which is an anonymized dump of all user-contributed content on the Stack Exchange network.
 
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