update text-to-speech README

Author: x4nth055

Diff for: machine-learning/text-to-speech/README.md

@@ -2,3 +2,4 @@
 - `pip3 install -r requirements.txt`
 - To convert text to speech online using Google API, use `tts_google.py`
 - To use offline engines in your platform, consider using `tts_pyttsx3.py`
+- To use transformers, use `tts_transformers.py`