Add P22 Underground font

flake.nix

@@ -73,6 +73,12 @@
             license = licenses.unfree;
             author = "Colophon Foundry";
           }
+          {
+            name = "P22 Underground";
+            dir = ./P22-Underground;
+            license = licenses.unfree;
+            author = "P22 Type Foundry";
+          }
           {
             name = "Caveat";
             files = [ ./Caveat.ttf ];