make example platform-independent and more obvious

doing something with the imported expression shows clearly that it has to be
read first

doc/manual/src/language/import-from-derivation.md

@@ -25,33 +25,33 @@ Building during evaluation can be disabled by setting [`allow-import-from-deriva
 
 ## Example
 
-In the following Nix expression, the derivation `drv` produces a file containing `1` after `sleep`ing for 5 seconds.
-
-Since `1` is a valid Nix expression itself, it can be [`import`](./builtins.md#builtins-import)ed.
-That requires reading from the output [store path] of `drv`, which has to be [realise]d before its contents `1` can be evaluated.
-
-[store path]: ../glossary.md#gloss-store-path
+In the following Nix expression, the inner derivation `drv` produces a file containing `"hello"`.
 
 ```nix
 # IFD.nix
 let
   drv = derivation {
-    name = "expensive";
+    name = "hello";
     builder = /bin/sh;
-    args = [ "-c" "${/bin/sleep} 5; echo 1 > $out" ];
+    args = [ "-c" "echo \"hello\" > $out" ];
     system = builtins.currentSystem;
   };
-in import drv
+in "${import drv} world"
 ```
 
 ```shellSession
 nix-instantiate IFD.nix --eval --read-write-mode
 ```
 
-    building '/nix/store/6n1mbib4n8l35ncfrbk8g8b3y14c7bi7-expensive.drv'...
-    1
+    building '/nix/store/348q1cal6sdgfxs8zqi9v8llrsn4kqkq-hello.drv'...
+    "hello world"
 
 
+Since `"hello"` is a valid Nix expression, it can be [`import`](./builtins.md#builtins-import)ed.
+That requires reading from the output [store path] of `drv`, which has to be [realise]d before its contents can be read and evaluated.
+
+[store path]: ../glossary.md#gloss-store-path
+
 ## Illustration
 
 The following diagram shows how evaluation is interrupted by a build, if the value of a Nix expression specifying a derivation depends on the result of another derivation.