[real-world uses] Add SourceCoder 3

doc/realworld.html

@@ -138,6 +138,7 @@
       <li><a href="http://snaptomato.appspot.com/editor.html">Snap Tomato</a> (HTML editing/testing page)</li>
       <li><a href="http://snippets.pro/">Snippets.pro</a> (code snippet sharing)</li>
       <li><a href="http://www.solidshops.com/">SolidShops</a> (hosted e-commerce platform)</li>
+      <li><a href="http://www.cemetech.net/sc/">SourceCoder 3</a> (online calculator IDE and editor)</li>
       <li><a href="http://sqlfiddle.com">SQLFiddle</a> (SQL playground)</li>
       <li><a href="http://www.subte.org/page/programar-ta-te-ti-online/">SubTe</a> (AI bot programming environment)</li>
       <li><a href="http://xuanji.appspot.com/isicp/">Structure and Interpretation of Computer Programs</a>, Interactive Version</li>