add some docs for rtorrent; add qbittorrent as another option

nix/home/programs/rtorrent/default.nix

@@ -1,6 +1,8 @@
 { pkgs, finalDir, downloadDir, watchDir }:
 let
-  dhtPort = 40000;
+  # this needs to be configured in mullvad's settings
+  dhtPort = 55358;
+  rtorrentPort = 54945;
 in
 {
 
@@ -10,6 +12,8 @@ in
 
   services.rtorrent = {
     enable = true;
+    port = rtorrentPort;
+    openFirewall = true;
     downloadDir = downloadDir;
     # flood needs to be able to access the datadir
     dataDir = downloadDir;
@@ -24,11 +28,11 @@ in
 
   networking.firewall = {
     allowedTCPPorts = [
-      # rtorrent default
-      50000
+      dhtPort
     ];
     allowedUDPPorts = [
       dhtPort
+      rtorrentPort
     ];
   };
 }