Provide Microsoft.AspNetCore.SignalR.Client package README (#57718)

Author: MackinnonBuck

src/SignalR/clients/csharp/Client/src/PACKAGE.md

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+## About
+
+`Microsoft.AspNetCore.SignalR.Client` provides the .NET client for ASP.NET Core SignalR, which simplifies adding real-time web functionality to apps.
+
+## Key Features
+
+SignalR provides the following capabilities:
+* Automatic connection management
+* Sending messages to all connected clients simultaneously
+* Sending messages to specific clients or groups of clients
+* Scaling to handle increasing traffic
+
+## How to Use
+
+To use `Microsoft.AspNetCore.SignalR.Client`, follow these steps:
+
+### Installation
+
+```shell
+dotnet add package Microsoft.AspNetCore.SignalR.Client
+```
+
+### Configuration
+
+See the [ASP.NET Core SignalR docs](https://learn.microsoft.com/aspnet/core/signalr/hubs) for information about how to configure SignalR hubs on the server.
+
+Then, you can configure the client to connect to the hub. For example:
+
+```csharp
+var connection = new HubConnectionBuilder()
+    .WithUrl("http://localhost:53353/Chat")
+    .Build();
+
+connection.On("ReceiveMessage", (string user, string message) =>
+{
+    Console.WriteLine($"{user}: {message}");
+});
+
+await connection.StartAsync();
+```
+
+## Main Types
+
+The main types provided by `Microsoft.AspNetCore.SignalR.Client` include:
+* `HubConnectionBuilder`: Provides an abstraction to construct new SignalR hub connections
+* `HubConnection`: Defines methods for managing a hub connection, including:
+  * Starting and stopping the connection
+  * Sending and receiving messages
+  * Handling disconnects and attempting reconnects
+* `HubConnectionOptions`: Provides options for configuring a `HubConnection`
+
+## Additional Documentation
+
+For additional documentation and examples, refer to the [official documentation](https://learn.microsoft.com/aspnet/core/signalr/dotnet-client) on the .NET client for ASP.NET Core SignalR.
+
+## Feedback & Contributing
+
+`Microsoft.AspNetCore.SignalR.Client` is released as open-source under the [MIT license](https://licenses.nuget.org/MIT). Bug reports and contributions are welcome at [the GitHub repository](https://github.com/dotnet/aspnetcore).