update some option descriptions

modules/docs.nix

@@ -120,7 +120,7 @@ in {
     in {
       enable = lib.mkOption {
         type = lib.types.bool;
-        description = "This option enables documentation for the flake, which is generated with Material for mkDocs and hosted by nginx at localhost:${defaultPort} by default.";
+        description = "Whether to enable documentation for the flake, generated with [Material for mkDocs](https://squidfunk.github.io/mkdocs-material/) and hosted by (containerised) nginx at localhost:${defaultPort} by default.";
         default = true;
       };
 
@@ -128,6 +128,7 @@ in {
         type = lib.types.str;
         description = "This option sets the port used by the nginx server hosting the local documentation site.";
         default = defaultPort;
+        readOnly = true;
       };
     };
   })) ];