vcpkg workflow depicts not-existent 'save/restore cache actions'

[lukka]

the workflow chart for the run-vcpkg task contains two errors: the initial restore cache, and the final 'save cache', both of them are not existing in this task.

Those are only available on the run-vcpkg GitHub action, for the Azure DevOps run-vcpkg task there is no automatic caching mechanism at all.

Documentation should be splitted in the shared submodule 'libs'.