Add Link to the Unofficial FTB Wiki

After a fair few questions from people joining my server, along with seeing a request in this reddit post: http://www.reddit.com/r/feedthebeast/comments/1d6it2/psa_wikia_vs_ftbwiki/ I had a go at adding a link to the FTB Wiki on the launcher. 

The image may need to be redone/rescaled as the text is on the small side, but the link is there now.

![Screenshot](http://i.imgur.com/wP1dsx9.png)