Add comment to explain string concatenation

packages/react/addons.js

@@ -1,6 +1,9 @@
 var warning = require('./lib/warning');
 warning(
   false,
+  // Require examples in this string must be split to prevent React's
+  // build tools from mistaking them for real requires.
+  // Otherwise the build tools will attempt to build a 'react-addons-{addon}' module.
   'require' + "('react/addons') is deprecated. " +
   'Access using require' + "('react-addons-{addon}') instead."
 );