Add placeholder Plugin Marketplace Manage screen #4053

plugins/CorePluginsAdmin/templates/extend.twig

+{% extends 'admin.twig' %}
+
+{% import '@CorePluginsAdmin/macros.twig' as plugins %}
+
+{% block content %}
+    <div style="max-width:980px;">
+
+        <h2>Extend Piwik with Plugins and Themes</h2>
+
+        <p>This page will let you download and install new Plugins from the Plugins Marketplace.
+            The <a href='?module=Proxy&action=redirect&url=http://plugins.piwik.org/' target='_blank'>Marketplace</a> is where
+                developers publish their plugins and themes to make them available to all Piwik users.</p>
+
+        <i>Note: all plugins are available for free at present; in the future we will enable Paid Plugins in the Marketplace
+            (<a href='mailto:hello@piwik.org?subject=Marketplace - Sell Plugin'>contact us</a> for early access).
+        </i>
+    </div>
+{% endblock %}