nixos/*: use properly indented strings for option docs

using regular strings works well for docbook because docbook is not as
whitespace-sensitive as markdown. markdown would render all of these as
code blocks when given the chance.

nixos/modules/services/development/jupyter/default.nix

@@ -149,13 +149,14 @@ in {
           };
         }
       '';
-      description = "Declarative kernel config
+      description = ''
+        Declarative kernel config.
 
-      Kernels can be declared in any language that supports and has the required
-      dependencies to communicate with a jupyter server.
-      In python's case, it means that ipykernel package must always be included in
-      the list of packages of the targeted environment.
-      ";
+        Kernels can be declared in any language that supports and has the required
+        dependencies to communicate with a jupyter server.
+        In python's case, it means that ipykernel package must always be included in
+        the list of packages of the targeted environment.
+      '';
     };
   };