add new goal to introduction

Author: michaelficarra

proposal.html

@@ -42,6 +42,12 @@ <h2>Goals</h2>
     <li>for functions created dynamically (through the *Function* and *GeneratorFunction* constructors), `toString` must synthesise a source text
     <li>for all other objects, `toString` must throw a *TypeError* exception
   </ul>
+
+  <p>The goals were revised yet again to include</p>
+
+  <ul>
+    <li>implementations must not be required to retain source text for all functions defined using ECMAScript code
+  </ul>
 </emu-intro>