add shortcode for prereg

Signed-off-by: Toshaan Bharvani <toshaan@vantosh.com>

themes/openpowerfoundation/layouts/shortcodes/prereg.html

@@ -0,0 +1,15 @@
+{{ $eventorganizer := .Get "organizer" }}
+{{ $eventcode := .Get "event" }}
+
+<link rel="stylesheet" type="text/css" href="https://registration.openpower.foundation/{{ $eventorganizer }}/{{ $eventcode }}/widget/v1.css">
+
+<div class="pretix-widget-compat" event="https://registration.openpower.foundation/{{ $eventorganizer }}/{{ $eventcode }}/"></div>
+<noscript>
+	<div class="pretix-widget">
+		<div class="pretix-widget-info-message">
+			JavaScript is disabled in your browser. To access our ticket shop without JavaScript,
+			please <a target="_blank" rel="noopener" href="https://registration.openpower.foundation/{{ $eventorganizer }}/{{ $eventcode }}/">click here</a>.
+		</div>
+	</div>
+</noscript>
+