Document that useAsCStringLen does not append NUL

System/OsPath/Data/ByteString/Short/Internal.hs

@@ -164,10 +164,14 @@ useAsCString bs action =
       action buf
   where l = length bs
 
--- | /O(n) construction./ Use a @ShortByteString@ with a function requiring a @CStringLen@.
--- As for @useAsCString@ this function makes a copy of the original @ShortByteString@.
+-- | /O(n) construction./ Use a @ShortByteString@ with a function requiring a 'CStringLen'.
+-- As for 'useAsCString' this function makes a copy of the original @ShortByteString@.
 -- It must not be stored or used after the subcomputation finishes.
 --
+-- Beware that this function does not add a terminating @\NUL@ byte at the end of 'CStringLen'.
+-- If you need to construct a pointer to a null-terminated sequence, use 'useAsCString'
+-- (and measure length independently if desired).
+--
 -- @since 0.10.10.0
 useAsCStringLen :: ShortByteString -> (CStringLen -> IO a) -> IO a
 useAsCStringLen bs action =