Add doc links

README.md

@@ -6,14 +6,17 @@
 [![Coverage Status](https://coveralls.io/repos/r9y9/pysptk/badge.svg?branch=master&service=github)](https://coveralls.io/github/r9y9/pysptk?branch=master)
 [![Documentation Status](https://readthedocs.org/projects/pysptk/badge/?version=latest)](https://readthedocs.org/projects/pysptk/?badge=latest)
 [![License](http://img.shields.io/badge/license-MIT-brightgreen.svg?style=flat)](LICENSE.md)
+[![][docs-stable-img]][docs-stable-url]
+[![][docs-latest-img]][docs-latest-url]
 
 A python wrapper for [Speech Signal Processing Toolkit (SPTK)](http://sp-tk.sourceforge.net/).
 
 **NOTE**: pysptk is based on a modified version of SPTK ([r9y9/SPTK](https://github.com/r9y9/SPTK)).
 
 ## Documentation
 
-See http://pysptk.readthedocs.org/ for the complete documentation.
+- [**STABLE**][docs-stable-url] — **most recently tagged version of the documentation.**
+- [**LATEST**][docs-latest-url] — *in-development version of the documentation.*
 
 ## Demonstration notebook
 
@@ -34,4 +37,10 @@ If yout want the latest master, run
 pip install git+https://github.com/r9y9/pysptk
 ```
 
-or clone the repository and then build it yourself.
+or clone the repository and then build it yourself.
+
+[docs-latest-img]: https://img.shields.io/badge/docs-latest-blue.svg
+[docs-latest-url]: https://pysptk.readthedocs.io/en/latest/
+
+[docs-stable-img]: https://img.shields.io/badge/docs-stable-blue.svg
+[docs-stable-url]: https://pysptk.readthedocs.io/en/stable/