doc: add parentheses to function and move reference

Add parentheses as `unref()` is a function. Move it to the correct
lexically-sorted location in the reference list.

doc/api/readline.md

@@ -638,7 +638,7 @@ will not terminate until it receives `EOF` (<kbd>Ctrl</kbd>+<kbd>D</kbd> on
 Linux/macOS, <kbd>Ctrl</kbd>+<kbd>Z</kbd> followed by <kbd>Return</kbd> on
 Windows).
 If you want your application to exit without waiting for user input, you can
-[`unref`][] the standard input stream:
+[`unref()`][] the standard input stream:
 
 ```js
 process.stdin.unref();
@@ -978,5 +978,5 @@ const { createInterface } = require('readline');
 [`process.stdin`]: process.md#process_process_stdin
 [`process.stdout`]: process.md#process_process_stdout
 [`rl.close()`]: #readline_rl_close
+[`unref()`]: net.md#net_socket_unref
 [reading files]: #readline_example_read_file_stream_line_by_line
-[`unref`]: net.md#net_socket_unref