Triplet links in docs/building-with-vcpkg documentation are outdated.

[Pravila00]

The links of Using triplets building-with-vcpkg section are outdated. They are pointing to an unexisting endpoint.

Specifically:

• https://vcpkg.readthedocs.io/en/latest/users/triplets/
• https://vcpkg.readthedocs.io/en/latest/examples/overlay-triplets-linux-dynamic/#overlay-triplets-example

Also, "Overlay triplets" are referred as "Custom triplets" which could be a bit confusing for Vcpkg users, as the official term is Overlay triplets