add javaunion in showcase

docs/content/showcase/javaunion.md

@@ -0,0 +1,15 @@
+---
+lastmod: 2016-01-20
+date: 2016-01-20T01:28:16+08:00
+description: "Java Union provide java tutorials for java beginer and you can run java program online"
+license: ""
+licenseLink: ""
+sitelink: http://www.javaunion.com/
+tags:
+- tutorials
+- java
+- online compile and run 
+- many examples
+thumbnail: /img/javaunion-tn.png
+title: Java Union
+---