examples : add embd_to_audio to tts-outetts.py [no ci] (#11235)

examples : add embd_to_audio to tts-outetts.py [no ci] (#11235)

This commit contains a suggestion for adding the missing embd_to_audio
function from tts.cpp to tts-outetts.py. This introduces a depencency
numpy which I was not sure if that is acceptable or not (only PyTorch
was mentioned in referened PR).

Also the README has been updated with instructions to run the example
with llama-server and the python script.

Refs: https://github.com/ggerganov/llama.cpp/pull/10784#issuecomment-2548377734