Update README.md

Here's the Finnish voice for the Piper text-to-speech system.

This model's been trained from scratch using a dataset created by the F5-TTS Finnish model, and the voice is the same as the makers' own, but it's been cloned using F5-TTS.

README.md

@@ -3,4 +3,6 @@ license: cc-by-nc-4.0
 language:
 - fi
 pipeline_tag: text-to-speech
+base_model:
+- rhasspy/piper-voices
 ---