add readthedocs badge

diff --git a/README.md b/README.md
index daa1f8d2c0c0e409185666ec4b3c0e8bf53cbb86..93e1755637a026513cb13c2963f273ded2b7f0ae 100644 (file)
--- a/README.md
+++ b/README.md
@@ -1,3 +1,4 @@
+[![Latest Docs](https://readthedocs.org/projects/pip/badge/?version=latest)](http://nlopt.readthedocs.io/en/latest/)
 [![Build Status](https://travis-ci.org/stevengj/nlopt.svg?branch=master)](https://travis-ci.org/stevengj/nlopt)
 [![Build Status](https://ci.appveyor.com/api/projects/status/github/stevengj/nlopt?branch=master&svg=true)](https://ci.appveyor.com/project/StevenGJohnson/nlopt)