docs[patch]: Adds LangGraph and LangSmith links, adds more crosslinks between pages (#22656)

@baskaryan @hwchase17

docs/docs/tutorials/index.mdx

@@ -27,5 +27,20 @@ New to LangChain or to LLM app development in general? Read this material to qui
 - [Classify text into labels](/docs/tutorials/classification)
 - [Summarize text](/docs/tutorials/summarization)
 
+### LangGraph
+
+LangGraph is an extension of LangChain aimed at
+building robust and stateful multi-actor applications with LLMs by modeling steps as edges and nodes in a graph.
+
+LangGraph documentation is currently hosted on a separate site.
+You can peruse [LangGraph tutorials here](https://langchain-ai.github.io/langgraph/tutorials/).
+
+### LangSmith
+
+LangSmith allows you to closely trace, monitor and evaluate your LLM application.
+It seamlessly integrates with LangChain, and you can use it to inspect and debug individual steps of your chains as you build.
+
+LangSmith documentation is hosted on a separate site.
+You can peruse [LangSmith tutorials here](https://docs.smith.langchain.com/tutorials/).
 
 For a longer list of tutorials, see our [cookbook section](https://github.com/langchain-ai/langchain/tree/master/cookbook).