Add readme

Author: guerler

config/plugins/visualizations/example/README.md

@@ -0,0 +1,6 @@
+# Galaxy Charts Minimal Example
+
+This minimal example visualization shows the basic structure of a Galaxy visualization plugin.  
+To enable it, open `static/example.xml` and remove the `hidden='true'` attribute.
+
+[Click here to learn more.](https://charts.galaxyproject.org)