Add Yggdrasil network.

A Ygg node can look like this: https://ygg.tlbs.ai

README.md

@@ -177,6 +177,7 @@ But you can write your own solutions for these problems using WireGuard under th
  - [TINC](https://www.tinc-vpn.org/): haven't tried it yet, but it doesn't work on iOS, worst case scenario I could live
  - [VPNCloud](https://github.com/dswd/vpncloud): similar properties to WireGuard, with more auto-mesh features
  - [cjdns](https://github.com/cjdelisle/cjdns): haven't tried it yet, should I?
+ - [Yggdrasil network](https://yggdrasil-network.github.io/): It is lightweight, self-arranging, supported on multiple platforms and allows pretty much any IPv6-capable application to communicate securely with other Yggdrasil nodes.
  - [ZeroTier](https://www.zerotier.com): haven't tried it yet, should I
  - [MeshBird](https://github.com/meshbird/meshbird): "Cloud native" VPN/networking layer