Update README.md

Author: chutchinson

README.md

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 Unofficial development of the RPG Toolkit Development System 4.x (rpgtoolkit.net).
 
+[![Build status](https://ci.appveyor.com/api/projects/status/hkvmpmrpcily4hws?svg=true)](https://ci.appveyor.com/project/chutchinson/rpgtk4)
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 # License
 
 Mozilla Public License 2.0