add Gluetun (#557)

Co-authored-by: nodiscc <nodiscc@gmail.com>

README.md

@@ -702,6 +702,7 @@ VPN software.
 - [DefGuard](https://defguard.net/) - True enterprise WireGuard with MFA/2FA and SSO. ([Source Code](https://github.com/DefGuard)) `Apache-2.0` `Rust`
 - [Dockovpn](https://dockovpn.io) - Out-of-the-box stateless dockerized OpenVPN server which starts in less than 2 seconds. ([Source Code](https://github.com/dockovpn/dockovpn)) `GPL-2.0` `Docker`
 - [Firezone](https://www.firezone.dev/) - WireGuard based VPN Server and Firewall. ([Source Code](https://github.com/firezone/firezone)) `Apache-2.0` `Docker`
+- [Gluetun VPN client](https://github.com/qdm12/gluetun) -  VPN client in a thin Docker container for multiple VPN providers, written in Go, and using OpenVPN or Wireguard, DNS over TLS, with a few proxy servers built-in.  `MIT` `docker`
 - [Headscale](https://github.com/juanfont/headscale) - Self-hostable fork of [Tailscale](https://tailscale.com), cross-platform clients, simple to use, built-in (currently experimental) monitoring tools. `BSD-3-Clause` `Go`
 - [Nebula](https://github.com/slackhq/nebula) - A scalable p2p VPN with a focus on performance, simplicity and security. `MIT` `Go`
 - [ocserv](https://www.infradead.org/ocserv/) - Cisco AnyConnect-compatible VPN server. ([Source Code](https://gitlab.com/ocserv/ocserv)) `GPL-2.0` `C`