feat(developer): add developer docs section for monetizing apps

Signed-off-by: Edward Ly <contact@edward.ly>

developer_manual/app_publishing_maintenance/index.rst

@@ -10,6 +10,7 @@ Transforming source files into a deliverable is documented in the :ref:`app-rele
    maintainer
    release_process
    Publishing App on the App Store <https://nextcloudappstore.readthedocs.io/en/latest/developer.html>
+   monetizing
    publishing
    code_signing
    release_automation

developer_manual/app_publishing_maintenance/monetizing.rst

@@ -0,0 +1,40 @@
+.. _app-store-monetizing:
+
+===================
+Monetizing your app
+===================
+
+.. sectionauthor:: Edward Ly <contact@edward.ly>
+
+
+The Nextcloud app store offers various features that enable app developers to receive some financial compensation for their work.
+
+Donations
+---------
+
+App developers can add optional donation links/buttons that lead to configurable URLs.
+This could be done by adding one or more donation tags in the app's ``info.xml`` file::
+
+   <donation title="Donate to the developers with PayPal" type="paypal">https://paypal.com/example</donation>
+   <donation type="stripe">https://stripe.com/example</donation>
+   <donation>https://other.service.com/example</donation>
+
+The currently supported types include ``paypal`` and ``stripe``.
+Having a type will display the corresponding service logo next to the donation link (or a generic logo if the type is not specified or is set to ``other``).
+If a link/button title is not specified, it defaults to ``Donate to support this app``.
+These buttons will appear in the appstore and in the app settings, and clicking on them will open their links in a new browser tab.
+
+.. note:: All donations received go directly to the developers. Nextcloud does not keep any commissions.
+
+Enterprise support
+------------------
+
+App developers can also add an optional ``Request quote`` button that will be shown in the appstore and app settings.
+This button leads to the `Nextcloud sales form <https://nextcloud.com/get-a-quote/>`_ where enterprise support for the app can be requested.
+If Nextcloud receives an interesting request, the sales team will reach out to the developers to discuss a partnership to provide support together (similar to other apps such as Collabora and OnlyOffice).
+Enterprise support targets larger Nextcloud installations of 100 users or more.
+
+To enable or disable the button, head to the **Enterprise support** page in the appstore account settings and click on **Mark as supported/unsupported** as appropriate next to the desired apps.
+
+.. image:: ../images/enterprise-support-settings.png
+  :alt: enterprise support settings page