update memory (#15507)

docs/docs/modules/memory/index.mdx

@@ -2,7 +2,7 @@
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-# Memory
+# [Beta] Memory
 
 Most LLM applications have a conversational interface. An essential component of a conversation is being able to refer to information introduced earlier in the conversation.
 At bare minimum, a conversational system should be able to access some window of past messages directly.
@@ -12,6 +12,23 @@ We call this ability to store information about past interactions "memory".
 LangChain provides a lot of utilities for adding memory to a system.
 These utilities can be used by themselves or incorporated seamlessly into a chain.
 
+Most of memory-related functionality in LangChain is marked as beta. This is for two reasons:
+
+1. Most functionality (with some exceptions, see below) are not production ready
+
+2. Most functionality (with some exceptions, see below) work with Legacy chains, not the newer LCEL syntax.
+
+The main exception to this is the `ChatMessageHistory` functionality. This functionality is largely production ready and does integrate with LCEL.
+
+- [LCEL Runnables](/docs/expression_language/how_to/message_history): For an overview of how to use `ChatMessageHistory` with LCEL runnables, see these docs
+
+- [Integrations](/docs/integrations/memory): For an introduction to the various `ChatMessageHistory` integrations, see these docs
+
+
+
+
+## Introduction
+
 A memory system needs to support two basic actions: reading and writing.
 Recall that every chain defines some core execution logic that expects certain inputs.
 Some of these inputs come directly from the user, but some of these inputs can come from memory.