doc: use kbd element in os doc

Use kbd element for key strokes and remove extra parentheses.

PR-URL: nodejs#35656
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>

Author: Trott

doc/api/os.md

@@ -436,7 +436,7 @@ The following signal constants are exported by `os.constants.signals`.
   <tr>
     <td><code>SIGINT</code></td>
     <td>Sent to indicate when a user wishes to interrupt a process
-    (<code>(Ctrl+C)</code>).</td>
+    (<kbd>Ctrl</kbd>+<kbd>C</kbd>).</td>
   </tr>
   <tr>
     <td><code>SIGQUIT</code></td>