Add CI build status badges to README.md

These badges show the build status of the master branch. If the Travis or
Appveyor build fails, it can be seen directly on Github in the README.

diff --git a/README.md b/README.md
index 59a1c93f4de01c700428ee925d4acc0cea618af1..c01e75864af8094d82bbfc423c2d9269cddb7882 100644 (file)
--- a/README.md
+++ b/README.md
@@ -1,5 +1,8 @@
 # Graphviz - Graph Visualization Tools
 
+[![Linux build status](https://img.shields.io/travis/ellson/graphviz/master.svg?label=Linux)](https://travis-ci.org/ellson/graphviz)
+[![Windows Build Status](https://img.shields.io/appveyor/ci/ellson/graphviz/master.svg?label=Windows)](https://ci.appveyor.com/project/ellson/graphviz/branch/master)
+
 from AT&T Research and Lucent Bell Labs
 * http://www.graphviz.org/