Add doc link (#10)

README.md

@@ -1,5 +1,7 @@
 # Introduction
 
+**Documentation**: <https://k2-fsa.github.io/sherpa/ncnn/index.html>
+
 See <https://github.com/k2-fsa/sherpa>
 
 This repo uses [ncnn](https://github.com/tencent/ncnn) for running the neural