docs/markdown/Users.md:add meson-vcpkg (example project)

[andy5995]

Related to #3500, projected hosted by @Neumann-A

I thought about linking to this project somewhere in the docs, but doing a search for 'vcpkg' yielded no results.

[Neumann-A]

I don't think my example is the fully meson correct example yet.

you probably want to have either a vcpkg subdir with a meson.options or a vcpkg parent project (also having a meson.options) which encapsulates the project to build. Unfortunately I am not fluid enough in meson to chose the correct injection method.

There is a lot more to include considering:
https://github.com/microsoft/vcpkg/blob/51685e17d6982871e1e8bab164edfe16f7ae6866/scripts/buildsystems/vcpkg.cmake#L506-L520