The firmware for that Wifi card is non-free. Don't hold your breath and go
buy a replacing card that is supported (or a USB adapter). You can buy it at
ThinkPenguin's. It is the only reseller I am aware of that guarantees that
all the hardware it sells works with Linux-libre (hence any 100% free
GNU/Linux distributions such as Trisquel): http://libre.thinkpenguin.com/
By using the link I gave you, 25% of the benefits on your purchase are
donated to the Trisquel project. :-)
You can also search for compatible devices elsewhere but it is hard because a
same model can sometimes have its chipset (what matters) change over time.
However you can find second-hand devices where the seller specifies the
chipset. I recently bought this USB adapter and you can hope the chipset did
not change in between:
http://www.tp-link.com/en/products/details/?categoryid=243&model=TL-WN722N
