As mentioned, your card depends on proprietary firmware, and this will not be
included in Trisquel (that would undermine the whole point of Trisquel's
existence). The solution is either to do without wireless, or get a new
wireless card or USB wireless adapter that works with libre software. An easy
place to shop for libre software friendly hardware is Think Penguin:
https://libre.thinkpenguin.com
Alternatively, you can get the same "mini" adapter that Think Penguin sells
from here:
https://tehnoetic.com/tehnoetic-wireless-adapter-gnu-linux-libre-tet-n150