Add hidden credentials file to .gitignore.
Add hidden credentials file to .gitignore.

This is used by our review poster script. Since usernames are different
per developer, we should ignore this file.

finnergizer/Markus,WilsonChiang/Markus,jeremygoh/Markus,WilsonChiang/Markus,arkon/Markus,kmccoan/Markus,reidka/Markus,wkwan/Markus,david-yz-liu/Markus,reidka/Markus,benjaminvialle/Markus,reidka/Markus,MarkUsProject/Markus,arkon/Markus,Lysette/Markus,MarkUsProject/Markus,david-yz-liu/Markus,melneubert/Markus,david-yz-liu/Markus,reidka/Markus,ealonas/Markus,david-yz-liu/Markus,arkon/Markus,binuri/Markus,kmccoan/Markus,finnergizer/Markus,melneubert/Markus,binuri/Markus,binuri/Markus,melneubert/Markus,binuri/Markus,reidka/Markus,selyanhb/Markus,arkon/Markus,jeremygoh/Markus,ealonas/Markus,Lysette/Markus,kmccoan/Markus,MarkUsProject/Markus,melneubert/Markus,MarkUsProject/Markus,wkwan/Markus,david-yz-liu/Markus,ealonas/Markus,david-yz-liu/Markus,wkwan/Markus,SoftwareDev/Markus,benjaminvialle/Markus,finnergizer/Markus,melneubert/Markus,reidka/Markus,jeremygoh/Markus,jeremygoh/Markus,WilsonChiang/Markus,finnergizer/Markus,Lysette/Markus,melneubert/Markus,WilsonChiang/Markus,wkwan/Markus,melneubert/Markus,MarkUsProject/Markus,kmccoan/Markus,benjaminvialle/Markus,SoftwareDev/Markus,Lysette/Markus,david-yz-liu/Markus,benjaminvialle/Markus,ealonas/Markus,david-yz-liu/Markus,binuri/Markus,finnergizer/Markus,finnergizer/Markus,WilsonChiang/Markus,SoftwareDev/Markus,Lysette/Markus,arkon/Markus,jeremygoh/Markus,selyanhb/Markus,Lysette/Markus,ealonas/Markus,ealonas/Markus,Lysette/Markus,wkwan/Markus,ealonas/Markus,ealonas/Markus,selyanhb/Markus,selyanhb/Markus,selyanhb/Markus,SoftwareDev/Markus,selyanhb/Markus,selyanhb/Markus,SoftwareDev/Markus,arkon/Markus,reidka/Markus,wkwan/Markus,jeremygoh/Markus,ealonas/Markus,SoftwareDev/Markus,jeremygoh/Markus,arkon/Markus,wkwan/Markus,melneubert/Markus,kmccoan/Markus,WilsonChiang/Markus,finnergizer/Markus,MarkUsProject/Markus,finnergizer/Markus,binuri/Markus,WilsonChiang/Markus,benjaminvialle/Markus,binuri/Markus,benjaminvialle/Markus,melneubert/Markus,binuri/Markus,reidka/Markus,kmccoan/Markus,binuri/Markus,finnergizer/Markus,MarkUsProject/Markus,wkwan/Markus,david-yz-liu/Markus,jeremygoh/Markus,selyanhb/Markus,jeremygoh/Markus,WilsonChiang/Markus,SoftwareDev/Markus,arkon/Markus,kmccoan/Markus,reidka/Markus,benjaminvialle/Markus,WilsonChiang/Markus,MarkUsProject/Markus,arkon/Markus,wkwan/Markus