Update pakistan.html

Pakistan mailing list is now live, lets add it! :)
It should still use the text "Mailing list" and only change the href, so it would be:

<code>&lt;li&gt;&lt;a href="https://lists.mozilla.org/listinfo/community-pakistan" class="email"&gt;{{ _('Mailing list') }}&lt;/a&gt;&;lt;/li&gt;</code>