Add C API for offline TTS. (#373)

c-api-examples/README.md

@@ -6,4 +6,13 @@ Please refer to the documentation
 https://k2-fsa.github.io/sherpa/onnx/c-api/index.html
 for details.
 
+
+## File descriptions
+
+- [decode-file-c-api.c](./decode-file-c-api.c) This file shows how to use the C API
+  for speech recognition with a streaming model.
+
+- [offline-tts-c-api.c](./offline-tts-c-api.c) This file shows how to use the C API
+  to convert text to speech with a non-streaming model.
+
 [sherpa-onnx]: https://github.com/k2-fsa/sherpa-onnx