[tutorial] update notes for TransformerEngine (#3098)

examples/tutorial/fp8/mnist/README.md

-# Basic MNIST Example with optional FP8
+# Basic MNIST Example with optional FP8 of TransformerEngine
+
+[TransformerEngine](https://github.com/NVIDIA/TransformerEngine) is a library for accelerating Transformer models on NVIDIA GPUs, including using 8-bit floating point (FP8) precision on Hopper GPUs, to provide better performance with lower memory utilization in both training and inference.
+
+Thanks for the contribution to this tutorial from NVIDIA. 
 
 ```bash
 python main.py
 python main.py --use-te   # Linear layers from TransformerEngine
 python main.py --use-fp8  # FP8 + TransformerEngine for Linear layers
 ```
+
+> We are working to integrate it with Colossal-AI and will finish it soon.