Add blogpost/docs for wireguard with VRFs in Linux

[margau]

Hi, for some time, I've had issues with wireguard and VRFs (the Routing Isolation Layer available in Linux, think of it as VLANs of Layer 3/IP). After figuring out how this works, I've written a Blogpost detailing how this works cleanly:

https://margau.net/posts/2024-01-12-wireguard-vrf/

This could possibly benefit some Wireguard users, especially on Linux servers and routers. Because this is my own work, I'd like to ask if this is "in scope" and okay to add before just opening an PR. Thanks!