doc: added README

Author: egbakou

README.md

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+
+
+<div style="text-align:center"><img src="art/logo.png" width=140 /></div>
+
+# FileSizeFromBase64.NET
+
+A .NET Standard 2.1 project containing a single method to **get file size from base64 string**. The base64 string can contain MIME-type or not. Paddings are also supported in the decoding process, you can define whether the paddings rules should be applied or not.
+
+## Installation
+
+You can install the NuGet Package in any .NET Project: .NET, .NET Standard, .NET Core, .NET 5 & 6, Xamarin, Maui, ... etc.
+
+ FileSizeFromBase64.NET can be [found here on NuGet](https://www.nuget.org/packages/FileSizeFromBase64.NET/) and can be installed by copying and pasting the following command into your Package Manager Console within Visual Studio (Tools > NuGet Package Manager > Package Manager Console).
+
+```powershell
+Install-Package FileSizeFromBase64.NET
+```
+
+Alternatively, if you're using .NET Core then you can install FileSizeFromBase64.NET via the CLI with the following command:
+
+```powershell
+dotnet add package FileSizeFromBase64.NET
+```
+
+## Documentation
+
+```csharp
+using FileSizeFromBase64.NET;
+
+var fileSize = FileSizeHelpers.GetFileSizeFromBase64String(string base64String, bool applyPaddingsRules, UnitsOfMeasurement unitsOfMeasurement)
+```
+
+| Parameters           | Data type |                         Description                          |       Default Value       |
+| :------------------- | :-------: | :----------------------------------------------------------: | :-----------------------: |
+| `base64String`       |  string   |           The base64 representation  of the file.            |                           |
+| `applyPaddingsRules` |  boolean  | [Base64 - Padding](https://en.wikipedia.org/wiki/Base64#Output_padding) |          `false`          |
+| `unitsOfMeasurement` |   Enum    | The unit of measurement for the file size returned by the method: `UnitsOfMeasurement.Byte`, `UnitsOfMeasurement.KiloByte`, `UnitsOfMeasurement.MegaByte` | `UnitsOfMeasurement.Byte` |
+
+## Usage
+
+```csharp
+using FileSizeFromBase64.NET;
+
+// File hello-world.txt => Size = 13 Bytes, Content: Hello world !
+var base64String = "data:text/plain;base64,SGVsbG8gd29ybGQgIQ==";
+
+var fileSize = FileSizeHelpers.GetFileSizeFromBase64String(base64String, true);
+Console.WriteLine($"File size: {fileSize}")
+    
+var fileSizeInKB = FileSizeHelpers.GetFileSizeFromBase64String(base64String, true, UnitsOfMeasurement.KiloByte);
+
+var fileSizeInMB = FileSizeHelpers.GetFileSizeFromBase64String(base64String, true, UnitsOfMeasurement.MegaByte);
+```
+
+
+
+## Created by: Laurent Egbakou
+
+- LinkedIn: [Laurent Egbakou](https://www.linkedin.com/in/laurentegbakou/)
+- Twitter: [@lioncoding](https://twitter.com/lioncoding)
+
+## License
+
+The MIT License (MIT) see [License file](https://github.com/lioncoding-oss/FileSizeFromBase64.NET/blob/main/LICENSE)
+
+## Contribution
+
+Feel free to create issues and PRs 😃