Update README.md

Added an Open Source Point of Sale system.

README.md

@@ -544,6 +544,7 @@ _Recipe management_
 - [OpenCart](https://www.opencart.com) - Free open source shopping cart solution. ([Source Code](https://github.com/opencart/opencart)) `GPL-3.0` `PHP`
 - [Open Classifieds](http://open-classifieds.com/) - Free open-source, self-hosted CMS for classifieds sites. ([Source Code](https://github.com/open-classifieds/openclassifieds2)) `GPL-3.0` `PHP`
 - [Open eShop](https://open-eshop.com/) - Sell your digital goods with licenses and provide support. ([Source Code](https://github.com/open-classifieds/open-eshop)) `GPL-3.0` `PHP`
+- [Open Source POS](https://www.opensourcepos.org/) - Open Source Point of Sale is a web based point of sale system. ([Source Code](https://github.com/opensourcepos/opensourcepos)) `MIT` `PHP`
 - [Osclass](https://osclass.org/) - One-stop shop to building your own classifieds marketplace. ([Source Code](https://github.com/osclass/Osclass)) `Apache-2.0` `PHP`
 - [OXID eShop](http://oxidforge.org) - OXID eShop is a flexible open source e-commerce software with a wide range of functionalities. ([Demo](http://demoshop.oxid-esales.com/community-edition/), [Source Code](https://github.com/OXID-eSales/oxideshop_ce)) `GPL-3.0` `PHP`
 - [Open Food Network](https://openfoodnetwork.org/) - Online marketplace for local food. It enables a network of independent online food stores that connect farmers and food hubs with individuals and local businesses. ([Source Code](https://github.com/openfoodfoundation/openfoodnetwork)) `AGPL-3.0` `Ruby`