Update README.md

Author: balisujohn

README.md

@@ -29,7 +29,7 @@ This is tested with Ubuntu 22.04 and cuda 12.0 and a 1070ti
 
 # Running
 
-**it's best to try short phrases first in GPU mode; long phrases fail in GPU mode with low VRAM**
+**Only lowercase letters, spaces, and punctuation are supported in the prompt.**
 
 You will need to place `ggml-model.bin`, `ggml-vocoder-model.bin` and `ggml-diffusion-model.bin` in the models directory to run tortoise.cpp. You can download them here https://huggingface.co/balisujohn/tortoise-ggml. I will release scripts for generating these files from tortoise-tts.