docs(langchain): update reference documentation to note moved embeddings modules (#33600)

Author: mdrxy

libs/langchain_v1/langchain/embeddings/__init__.py

@@ -4,6 +4,12 @@
     This page contains **reference documentation** for Embeddings. See
     [the docs](https://docs.langchain.com/oss/python/langchain/retrieval#embedding-models)
     for conceptual guides, tutorials, and examples on using Embeddings.
+
+!!! warning "Modules moved"
+    With the release of `langchain 1.0.0`, several embeddings modules were moved to
+    `langchain-classic`, such as `CacheBackedEmbeddings` and all community
+    embeddings. See [list](https://github.com/langchain-ai/langchain/blob/bdf1cd383ce36dc18381a3bf3fb0a579337a32b5/libs/langchain/langchain/embeddings/__init__.py)
+    of moved modules to inform your migration.
 """
 
 from langchain_core.embeddings import Embeddings