Disable man caches

hosts/modules/base.nix

@@ -11,6 +11,11 @@
     shell = pkgs.fish;
   };
 
+  # this is to avoid some problem that happens apparently only when fish is
+  # enabled, where generating man cahes takes a very long time. note that it may
+  # break fish man completion and apropos.
+  documentation.man.generateCaches = false;
+
   # enable a 1GB swap file
   swapDevices = [{
     device = "/swapfile";