Add vcpkg installation instructions

[Adela0814]

cpu_features available as a port in vcpkg, a C++ library manager that simplifies installation for cpu_features and other project dependencies. Documenting the install process here will help users get started by providing a single set of commands to build cpu_features, ready to be included in their projects.

We also test whether our library ports build in various configurations (dynamic, static) on various platforms (OSX, Linux, Windows: x86, x64) to keep a wide coverage for users.

I'm a maintainer for vcpkg, and here is what the port script looks like. We try to keep the library maintained as close as possible to the original library.

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