Check if curl extension is available when installing

ext.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace mober\discordnotifications;
+
+class ext extends \phpbb\extension\base
+{
+	/**
+	 * {@inheritDoc}
+	 */
+	public function is_enableable()
+	{
+		$language = $this->container->get('language');
+		$language->add_lang('acp_discord_notifications', 'mober/discordnotifications');
+
+		$curl_available = extension_loaded('curl');
+		if (!$curl_available)
+		{
+			return $language->lang('DN_MISSING_CURL');
+		}
+
+		return true;
+	}
+}