chore: improve NuGet README examples for IOCTL/RPC consumer usage

[ntoskrnl7]

Summary

• Improve NuGet package README to remove outdated wording and align with NuGet/MSBuild usage.
• Add practical IOCTL and RPC sample pairs for kernel and app sides.
• Add shared contract header snippets for the examples (shared/demo_ioctl.hpp, shared/demo_rpc.hpp).
• Keep package description concise and include release artifact notes.