Add README documenting project overview and NuGet package usage

[Copilot]

The repository had no documentation explaining what the project does or how to consume its packages.

Changes

• Project overview — describes the three-package architecture and includes a flow diagram showing how Model, Persistence, and ServiceHost interact at runtime (client request → EF Core paginated query → X-Pagination response header)
• Per-package docs — for each NuGet package (Jaricardodev.Paginator.Model, .Persistence, .ServiceHost):
  • Install commands (dotnet add package / Install-Package)
  • Dependency notes
  • Realistic C# usage example
  • API reference table (public types, members, parameters)

Usage snapshot

// Persistence: paginate an EF Core query
var page = await _db.Products
    .AsNoTracking()
    .ToPaginatedListAsync(pageNumber, pageSize);

// ServiceHost: register the filter once; X-Pagination header is added automatically
builder.Services.AddControllers(options =>
    options.Filters.Add<AddPaginationHeaderResultFilter>());

HTTP/1.1 200 OK
X-Pagination: {"totalItemsCount":100,"totalPageCount":10}

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