Add README.md

Author: ScarletKuro

README.md

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+## Overview
+
+The `JsonDateTimeConverterAttribute` allows you to specify a custom date format for `DateTime`, `DateTimeOffset`, and their nullable counterparts when serializing and deserializing JSON using `System.Text.Json`. This ensures consistency in how date and time values are handled across your application.
+
+## Installation
+
+Ensure you have the necessary .NET target framework installed. This attribute is compatible with:
+- .NET 6
+- .NET 7
+- .NET 8
+
+## Usage
+
+### Example Model
+
+```csharp
+using System;
+using System.Text.Json.Serialization;
+using Scarlet.System.Text.Json.DateTimeConverter;
+
+public class MyModel
+{
+    [JsonDateTimeConverter("yyyy-MM-dd")]
+    public DateTime Date { get; set; }
+
+    [JsonDateTimeConverter("yyyy-MM-ddTHH:mm:ss.fffZ")]
+    public DateTimeOffset DateTimeOffset { get; set; }
+}
+```
+
+### Example Program
+
+```csharp
+using System;
+using System.Text.Json;
+
+public class Program
+{
+    public static void Main()
+    {
+        var model = new MyModel
+        {
+            Date = DateTime.Now,
+            DateTimeOffset = DateTimeOffset.Now
+        };
+
+        // Serialize
+        string jsonString = JsonSerializer.Serialize(model);
+        Console.WriteLine($"Serialized JSON: {jsonString}");
+
+        // Deserialize
+        var deserializedModel = JsonSerializer.Deserialize<MyModel>(jsonString);
+        Console.WriteLine($"Deserialized Date: {deserializedModel.Date}");
+        Console.WriteLine($"Deserialized DateTimeOffset: {deserializedModel.DateTimeOffset}");
+    }
+}
+```
+
+## Notes
+
+- The `JsonDateTimeConverterAttribute` can be applied to properties of type `DateTime`, `DateTime?`, `DateTimeOffset`, and `DateTimeOffset?`.
+- The format string provided to the attribute should follow the standard date and time format strings in .NET.