nixos: services: matrix: add Facebook bridge

I probably won't actually use it, after test-driving it quickly.

But now that the effort has been expanded, might as well keep it if only
as a future reference.

modules/nixos/services/matrix/default.nix

@@ -30,6 +30,10 @@ let
   '';
 in
 {
+  imports = [
+    ./bridges.nix
+  ];
+
   options.my.services.matrix = with lib; {
     enable = mkEnableOption "Matrix Synapse";