Added Invoice Ninja

Added Invoice Ninja - a self-hosted PHP based invoicing system based on Laravel using the AAL license (https://opensource.org/licenses/AAL).

README.md

@@ -511,6 +511,7 @@ Some [Groupware](#groupware) solutions also feature file sharing and synchroniza
   * [GLPI](http://www.glpi-project.org/spip.php?lang=en) - GLPI is an IT assests/resources/inventory manager ([Source code](https://forge.glpi-project.org/projects/glpi)) `GPLv2` `PHP`
   * [GRR](http://grr.devome.com/?lang=en) - Assets management and booking for small/medium companies ([demo](http://grr.devome.com/demo/week_all.php?year=2015&month=07&day=28&area=94), _administrateur/azerty_) `GPLv2` `PHP`
   * [Inventaire](https://inventaire.io/welcome) -  collaborative resources mapper project, while yet only focused on exploring books mapping with wikidata and ISBNs ([Source code](https://github.com/inventaire/inventaire)) `AGPLv3` `Nodejs`
+  * [Invoice Ninja](https://www.invoiceninja.com/) - A powerful tool to invoice clients online. ([Demo](https://app.invoiceninja.com/invoices/create), [Source code](https://github.com/invoiceninja/invoiceninja)) `AAL`
   * [InvoicePlane](https://invoiceplane.com/) - Manage quotes, invoices, payments and customers for your small business. ([Demo](https://demo.invoiceplane.com), [Source code](https://github.com/InvoicePlane/InvoicePlane)) `MIT`
   * [IHateMoney](http://ihatemoney.org/) - Manage your shared expenses, easily. ([Source code](https://github.com/spiral-project/ihatemoney)) `BSD` `Python`
   * [Tryton](http://www.tryton.org/) - Core base of a complete business solution (ERP). ([Demo](http://demo.tryton.org) admin/admin, [Source code](https://hg.tryton.org)) `GPLv3` `Python`