Add vcpkg installation instructions

[Adela0814]

cli11 is available as a port in vcpkg, a C++ library manager that simplifies installation for cli11 and other project dependencies. Documenting the install process here will help users get started by providing a single set of commands to build cli11, 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, UWP, ARM) 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.

[codecov[bot]]

Codecov Report

Base: 99.06% // Head: 99.06% // No change to project coverage :thumbsup:

Coverage data is based on head (132b06b) compared to base (1a26afa). Patch has no changes to coverable lines.

Additional details and impacted files

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  Coverage   99.06%   99.06%           
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  Files          16       16           
  Lines        3964     3964           
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  Hits         3927     3927           
  Misses         37       37           

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[jzakrzewski]

Sorry for the negativity, but I'm not convinced that the project should document something it does not control. Such things tend to get outdated pretty easily.

[henryiii]

I'd be okay to help make PRs to keep this up to date if it becomes a problem. I'm a little more worried about making the README grow too much. I think I'd rather add this to the gitbook, and then link to it from the readme. I also need to move the gitbook over to a non-dead renderer. Let's keep it open but on hold until we work on the docs a bit.

[siilky]

in the meanwhile, could we update vcpkg release version? It is still 2.2 there, which is a year old

[phlptp]

changes are included in #901