pi-hole: add source code link

README.md

@@ -359,7 +359,7 @@ _See also: [awesome-selfhosted/Database Management](https://github.com/awesome-s
 *DNS server control panels.*
 
 - [Atomia DNS](http://atomiadns.com/) - DNS management system. ([Source Code](https://github.com/atomia/atomiadns/))
-- [Pi-hole](https://pi-hole.net/) - A blackhole for Internet Advertisements with a gui for managing and monitoring
+- [Pi-hole](https://pi-hole.net/) - A blackhole for Internet Advertisements with a gui for managing and monitoring. ([Source Code](https://github.com/pi-hole/pi-hole))
 - [Poweradmin](http://www.poweradmin.org/) - Friendly web-based DNS administration tool for PowerDNS server.