Add amber-lang.net to real-world uses

doc/realworld.html

@@ -23,6 +23,7 @@
 
     <ul>
       <li><a href="http://brackets.io">Adobe Brackets</a> (code editor)</li>
+      <li><a href="http://amber-lang.net/">Amber</a> (JavaScript-based Smalltalk system)</li>
       <li><a href="http://bluegriffon.org/">BlueGriffon</a> (HTML editor)</li>
       <li><a href="http://cargocollective.com/">Cargo Collective</a> (creative publishing platform)</li>
       <li><a href="http://www.codebugapp.com/">Codebug</a> (PHP Xdebug front-end)</li>