doc: make clear the result of comparison between Symbol.for

PR-URL: nodejs/node#43309
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Akhil Marsonya <akhil.marsonya27@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>

doc/contributing/using-symbols.md

@@ -61,7 +61,7 @@ for different reasons.
 
 ```js
 const s = Symbol.for('hello');
-console.log(s === Symbol.for('hello'));
+console.log(s === Symbol.for('hello')); // true
 ```
 
 In the Node.js runtime we prefix all our global symbols with `nodejs.`,