Add tts document&fix bug (#2156)

Co-authored-by: luowei <glpat-EjySCyNjWiLqAED-YmwM>
Co-authored-by: crazywoola <427733928@qq.com>
Co-authored-by: crazywoola <100913391+crazywoola@users.noreply.github.com>
Co-authored-by: Yeuoly <45712896+Yeuoly@users.noreply.github.com>

api/core/model_runtime/README.md

@@ -13,6 +13,7 @@ This module provides the interface for invoking and authenticating various model
   - `Text Embedding Model` - Text Embedding, pre-computed tokens capability
   - `Rerank Model` - Segment Rerank capability
   - `Speech-to-text Model` - Speech to text capability
+  - `Text-to-speech Model` - Text to speech capability
   - `Moderation` - Moderation capability
 
 - Model provider display