Add Vcpkg to C++ installation instructions for Windows

[ras0219-msft]

Fixes issue #1154 by noting that vcpkg contains protobuf. Potential improvements: also remark how to use vcpkg to get dependencies when building from source via CMake.

[grpc-kokoro]

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[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

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[liujisi]

The change looks good. Could you sign the cla please?

[podsvirov]

Need add info about protobuf[zlib] feature package too.

[googlebot]

CLAs look good, thanks!

[ras0219-msft]

I signed it!

[liujisi]

Thanks!