readme: add maintenance warning (#491)

Co-authored-by: Luca Antiga <luca@lightning.ai>

README.md

@@ -3,16 +3,17 @@
 
 # ⚡ Lit-LLaMA ️
 
-<!--
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 ![cpu-tests](https://github.com/lightning-AI/lit-llama/actions/workflows/cpu-tests.yml/badge.svg) [![Build Status](https://dev.azure.com/Lightning-AI/lit%20Models/_apis/build/status%2FLightning-AI.lit-LLaMA?branchName=main)](https://dev.azure.com/Lightning-AI/lit%20Models/_build/latest?definitionId=49&branchName=main) [![license](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://github.com/Lightning-AI/lit-llama/blob/master/LICENSE) [![Discord](https://img.shields.io/discord/1077906959069626439?style=plastic)](https://discord.gg/VptPCZkGNa)
 
+<pre>
+<b>⚠️ Warning: Not Actively Maintained</b>
+
+This repository is no longer actively maintained. For a more up-to-date alternative, please visit the LitGPT project:
+<a href="https://github.com/Lightning-AI/litgpt">https://github.com/Lightning-AI/litgpt</a>, which serves as the successor to this repository.
+
+Feel free to explore, reuse, or fork, but be aware that no further updates or support will be provided.
+</pre>
+
 <img src="https://pl-public-data.s3.amazonaws.com/assets_lightning/Llama_pineapple.gif" alt="Lit-LLaMA and pineapple pizza" width="500px"/>
 
 </div>