add GLPI source code link

- ref. #416

README.md

@@ -451,7 +451,7 @@ _See also: [IT Asset Management]([Ralph](#it-asset-management))_
 
 *IT Assets Management software.*
 
-- [GLPI](https://www.glpi-project.org/) - Information Resource-Manager with an additional Administration Interface.
+- [GLPI](https://www.glpi-project.org/) - Information Resource-Manager with an additional Administration Interface. ([Source Code](https://github.com/glpi-project/glpi))
 - [OCS Inventory NG](https://ocsinventory-ng.org/) - Asset management and deployment solution for all devices in your IT Department. ([Source Code](https://github.com/OCSInventory-NG)) `GPL-2.0` `PHP/Perl`
 - [OPSI](http://www.opsi.org) - Hardware and software inventory, client management, deployment, and patching for Linux and Windows. ([Source Code](https://github.com/opsi-org/)) `GPL-3.0/AGPL-3.0` `OVF/Python`
 - [RackTables](http://racktables.org/) - Datacenter and server room asset management like document hardware assets, network addresses, space in racks, networks configuration. ([Source Code](https://github.com/RackTables/racktables), [Demo](https://www.racktables.org/demo.php)) `GPL-2.0` `PHP`