Add Internet Explorer 11 tiles

This adds information about IE 11 tiles for those who are hopelessly obsessive. :wink:

I'm still unclear on one piece of information in the documentation;

> Specifies the image to use as the medium tile, which is 150x150 pixels at 100% scaling.

I believe this means that it should actually be delivered in a larger format, however, I cannot find any Microsoft site which implements the IE11 tiles at this point to confirm the expected sizes.

According to [this KB article](http://msdn.microsoft.com/en-us/library/windows/apps/hh465362.aspx), for Windows Store apps, you're expected to support up to 180% scaling, so this might mean that the 150x150 `msapplication` image should actually be 270x270.

I don't think this is a problem in the immediate term, however, it might be worth investigating.