varnish: add source code link

README.md

@@ -751,7 +751,7 @@ _See also: [awesome-selfhosted/Database Management](https://github.com/awesome-s
 - [Lighttpd](https://www.lighttpd.net/) - Secure, fast, compliant, and very flexible web server that has been optimized for high-performance environments. ([Source Code](https://git.lighttpd.net/lighttpd/lighttpd1.4)) `C`
 - [Nginx](https://nginx.org/en/) - HTTP and reverse proxy server, mail proxy server, and generic TCP/UDP proxy server. ([Source Code](https://hg.nginx.org/nginx/file/tip))
 - [Traefik](https://traefik.io/) - HTTP reverse proxy and load balancer that makes deploying microservices easy. ([Source Code](https://github.com/traefik/traefik))
-- [Varnish](https://varnish-cache.org/) - Web application accelerator/caching HTTP reverse proxy.
+- [Varnish](https://varnish-cache.org/) - Web application accelerator/caching HTTP reverse proxy. ([Source Code](https://github.com/varnishcache/varnish-cache))
 
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