Updated inline config documentation

Added reference to trade header removal. This allows users to disable
the trade header at the top of the page by setting currency to an empty
string.

Addresses #305

public/include/config/global.inc.dist.php

@@ -61,7 +61,8 @@ $config['wallet']['password'] = 'testnet';
  * Explanation:
  *   mmcfe-ng will try to fetch the current exchange rates
  *   from this API URL/target. Currently btc-e and coinchoose
- *   are supported in mmcfe-ng.
+ *   are supported in mmcfe-ng. If you want to remove the trade
+ *   header just set currency to an empty string.
  *
  * Default (btc-e.com):
  *   url       =  `https://btc-e.com`