Update README.md

Author: monkstone

README.md

@@ -25,6 +25,8 @@ Many of the vanilla processing example sketches have been translated to ruby-pro
     2. [vecmath][]
     3. [control-panel][]
 
+4. [JBox2D][]
+
 [Learning Processing with Ruby]:https://github.com/ruby-processing/learning-processing-with-ruby
 [Nature of Code Examples in ruby]:https://github.com/ruby-processing/The-Nature-of-Code-Examples-in-Ruby
 [Basic]:https://github.com/ruby-processing/Example-Sketches/tree/master/samples/processing_app/basics
@@ -42,3 +44,4 @@ Many of the vanilla processing example sketches have been translated to ruby-pro
 [fastmath]:https://github.com/ruby-processing/Example-Sketches/tree/master/samples/processing_app/libraries/fastmath
 [vecmath]:https://github.com/ruby-processing/Example-Sketches/tree/master/samples/processing_app/libraries/vecmath
 [control-panel]:https://github.com/ruby-processing/Example-Sketches/tree/master/samples/contributed/jwishy.rb
+[JBox2D]:https://github.com/ruby-processing/Example-Sketches/tree/master/samples/external_library/ruby_gem/jbox2d