lenovo/t460s: add middle button config + comments (#14)

lenovo/t460s.nix

@@ -26,5 +26,34 @@
     { version = "4.6";   msg = "Suspending the T460s by closing the lid when running on battery causes the machine to freeze up entirely."; }
   ];
 
+  # For the wifi (intel iwlwifi)
   hardware.enableAllFirmware = true;
+
+  # For the screen. I don't know what to do with this information, but
+  # the hiDPI support is far from perfect (as of July 2016):
+
+  # Resolution: 2560 x 1440 px
+  # Size: 12.2" × 6.86" (30.99cm × 17.43cm)
+  # DPI: 209.8
+  # Dot Pitch: 0.1211mm
+  # Aspect Ratio: 16 × 9 (1.78:1)
+  # Pixel Count: 3,686,400
+  # Megapixels: 3.69MP
+
+  # Use libinput to let the physical middle button be used to scroll
+  # with the trackpoint
+  services.xserver = {
+    libinput.enable = true;
+    synaptics.enable = false;
+
+    config = ''
+      Section "InputClass"
+        Identifier     "Enable libinput for TrackPoint"
+        MatchIsPointer "on"
+        Driver         "libinput"
+        Option         "ScrollMethod" "button"
+        Option         "ScrollButton" "8"
+      EndSection
+    '';
+  };
 }