Add entry for golang.zx2c4.com/wireguard

[MikaelUrankar]

seen with net/yggdrasil: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=247045

 # Mirrors for the following packages are not currently known, please look them up and handle these tuples manually:
#       ::v0.0.20200320:group_name/vendor/golang.zx2c4.com/wireguard (from git.zx2c4.com/wireguard-go@v0.0.20200320)
#       ::v0.1.0:group_name/vendor/golang.zx2c4.com/wireguard/windows (from git.zx2c4.com/wireguard-windows@v0.1.0)

https://github.com/WireGuard/wireguard-go: Mirror only. Official repository is at https://git.zx2c4.com/wireguard-go

[dmgk]

Merged, thanks!