Update Neo2 documentation

Apparently, the listed simple modifications are also required for an
original, external Apple keyboard. [1]

[1]: https://git.neo-layout.org/neo/neo-layout/issues/671

public/extra_descriptions/neo2.json.html

@@ -69,7 +69,7 @@ <h3>Extension rules</h3>
 </table>
 <br /><br />
 
-To use a PC style keyboard, the following simple modifications need to be enabled:<br /><br />
+To use an external keyboard, the following simple modifications need to be enabled:<br /><br />
 
 <pre>
 grave_accent_and_tilde (`) -> non_us_backslash<br />