Add documentation how to use loadlink() options in edirom-edition XML navigatorDefinition

[bwbohl]

It would be great if it was possible to use the loadlink() syntax as described in https://github.com/Edirom/Edirom-Online/wiki/Links-to-Edirom-Online-and-its-content in the target attributes of the navigatorDefinition in the edirom-edition XML, e.g., to provide parameters like useExisting:true for opening contents in the same window.