add logo

Signed-off-by: Stefan Niederhauser <ghuder5@gmx.ch>

Author: nidi3

README.md

@@ -1,4 +1,4 @@
-# graphviz-java 
+# graphviz-java <img src="logo.png" height="100" align="middle">
 [![Build Status](https://travis-ci.org/nidi3/graphviz-java.svg)](https://travis-ci.org/nidi3/graphviz-java)
 [![codecov](https://codecov.io/gh/nidi3/graphviz-java/branch/master/graph/badge.svg)](https://codecov.io/gh/nidi3/graphviz-java)
 [![License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://opensource.org/licenses/Apache-2.0)