Apply suggestions from code review

Thanks @infinisil

Co-authored-by: Silvan Mosberger <[email protected]>

lib/options.nix

@@ -78,15 +78,16 @@ rec {
   /**
     Creates an Option attribute set. mkOption accepts an attribute set with the following keys:
 
-    All keys default to `null` when not given.
-
     # Inputs
 
     Structured attribute set
     : Attribute set containing none or some of the following attributes.
 
       `default`
       : Optional default value used when no definition is given in the configuration.
+      
+        _Default:_ None, when the option is evaluated an error is thrown.
+
 
 
       `defaultText`
@@ -96,7 +97,7 @@ rec {
       : Optional example value used in the manual.
 
       `description`
-      : Optional string describing the option.
+      : Optional string describing the option. This is required if option documentation is generated.
 
       `relatedPackages`
       : Optional related packages used in the manual (see `genRelatedPackages` in `../nixos/lib/make-options-doc/default.nix`).