README.md in natural_number_string-0.3.1 vs README.md in natural_number_string-1.0.0

@@ -1,8 +1,8 @@
 # NaturalNumberString
 
-[![Gem version][gem-image]][gem-url] [![Travis-CI Status][travis-image]][travis-url]
+[![Gem version][gem-image]][gem-url] [![Travis-CI Status][travis-image]][travis-url] [![yard docs][docs-image]][docs-url]
 
 > Check the string is a natural number.
 
 
 ## Usage
@@ -57,10 +57,12 @@
 *Required*
 
 value.
 
 
+And [details][docs-url].
+
 ## Changelog
 
 [changelog.md](./changelog.md).
 
 
@@ -101,5 +103,7 @@
 
 [travis-url]: https://travis-ci.org/packsaddle/ruby-natural_number_string
 [travis-image]: https://img.shields.io/travis/packsaddle/ruby-natural_number_string/master.svg?style=flat-square&label=build%20%28linux%29
 [gem-url]: https://rubygems.org/gems/natural_number_string
 [gem-image]: http://img.shields.io/gem/v/natural_number_string.svg?style=flat-square
+[docs-url]: http://www.rubydoc.info/gems/natural_number_string
+[docs-image]: https://img.shields.io/badge/yard-docs-blue.svg?style=flat-square