[javascript-lint addon] Add comment noting dependency

Added note on dependency on jshint.js

Author: erosman

addon/lint/javascript-lint.js

@@ -1,6 +1,8 @@
 // CodeMirror, copyright (c) by Marijn Haverbeke and others
 // Distributed under an MIT license: https://codemirror.net/LICENSE
 
+// Depends on jshint.js from https://github.com/jshint/jshint
+
 (function(mod) {
   if (typeof exports == "object" && typeof module == "object") // CommonJS
     mod(require("../../lib/codemirror"));