Update README.md

Author: samber

README.md

@@ -8,6 +8,9 @@ GPT2 and GPT3 use byte pair encoding to turn text into a series of integers to f
 
 This code was inspired by [Javascript implementation](https://github.com/latitudegames/GPT-3-Encoder) and partially generated by OpenAI himself!
 
+> [!WARNING]
+> This implementation of BPE tokenizer is not valid. See [https://x.com/burkov/status/1863007688470241336](https://x.com/burkov/status/1863007688470241336).
+
 ## Install
 
 ```bash