Update README.md

* added 'bare' option (short) documentation

Author: olivierphi

README.md

@@ -39,6 +39,7 @@ options:
 
   * **filename** - The source filename, formatted into error messages
   * **header** - Add a "Generated by..." header
+  * **bare** - If set to ```true```, the generated Javascript won't be embedded in a [IIFE](http://benalman.com/news/2010/11/immediately-invoked-function-expression/)
   * **rewrite** - Enable the rewriter (debugging)
   * **tokens** - Reference to token stream (debugging)
   * **trace** - File to write parser trace to (debugging)