[DOC] add donation section

README.md

@@ -13,3 +13,7 @@ List of repositories:
 * https://github.com/it-projects-llc/l10n-addons
 * https://github.com/it-projects-llc/odoo-telegram
 * https://github.com/it-projects-llc/odoo-saas-tools
+
+Donation
+========
+Feel free to support our efforts by purchasing [our mail modules at app store](https://apps.odoo.com/apps/modules/category/Discuss/browse?price=Paid&order=Newest&author=IT-Projects+LLC)