feat: generate mandb cache to use apropos and whatis

configs/default.nix

@@ -9,6 +9,9 @@ in {
     {
       boot.supportedFilesystems = [ "ntfs" ];
     }
+    {
+      documentation.man.generateCaches = true;
+    }
     {
       niveum.user = {
         github = "kmein";