docs: fixup description of builtins.importNative

Follow up documentation fix.

Change-Id: I135c2c323ad550c95d27ef854b7db334b851f29c

src/libexpr/eval-settings.hh

@@ -19,9 +19,9 @@ struct EvalSettings : Config
         Enable built-in functions that allow executing native code.
 
         In particular, this adds:
-        - `builtins.importNative` *path*
-        
-          Load a dynamic shared object (DSO) at *path* which exposes a function pointer to a procedure that initialises a Nix language value, and return that value.
+        - `builtins.importNative` *path* *symbol*
+          Runs function with *symbol* from a dynamic shared object (DSO) at *path*.
+          This may be used to add new builtins to the Nix language.
           The procedure must have the following signature:
           ```cpp
           extern "C" typedef void (*ValueInitialiser) (EvalState & state, Value & v);