docs(README): improve the "resources" section.

Author: pabroux

README.md

@@ -1,4 +1,4 @@
-# 🤖 LLM demo
+# 🐦‍⬛🔗 LangChain LangGraph Course
 
 <p align="left">
   <a href="https://github.com/pabroux/llm-demo/blob/master/LICENSE">
@@ -25,4 +25,21 @@ sample_llm_application : explains how to use LLM with LangChain (PromptTemplate
 
 ## Resources
 
+The resources described here are sorted in order of importance. For instance, to better understand and grasp each LangChain concept, you should have knowledge of LLM theory and LLM engineering.
+
+### LLM theory
+
+- [LLM course](https://github.com/mlabonne/llm-course?tab=readme-ov-file#-the-llm-scientist)
+
+### LLM engineering
+
+- [LLM's Engineer Handbook](https://www.amazon.com/LLM-Engineers-Handbook-engineering-production/dp/1836200072/?_encoding=UTF8&pd_rd_w=TdT64&content-id=amzn1.sym.46807d81-91bd-498b-9732-d523d8e7a752%3Aamzn1.symc.fc11ad14-99c1-406b-aa77-051d0ba1aade&pf_rd_p=46807d81-91bd-498b-9732-d523d8e7a752&pf_rd_r=ZRWE6KNJ1MWQT6JCGNQQ&pd_rd_wg=F82Rn&pd_rd_r=d1fd6111-7922-469e-8bb0-e0a31dd91141&ref_=pd_hp_d_atf_ci_mcx_mr_ca_hp_atf_d)
+
+### LangChain
+
+- [LangChain tutorial](https://python.langchain.com/docs/tutorials/)
+- [LangChain expression language (LCEL)](https://python.langchain.com/docs/versions/migrating_chains/llm_chain/#legacy)
+
+### LangGraph
+
 - [LangGraph tutorial](https://langchain-ai.github.io/langgraph/concepts/why-langgraph/)