add CLA signed badge

README.md

@@ -7,6 +7,7 @@
 [![MyGet (nightly builds)](https://img.shields.io/myget/abp-nightly/vpre/Volo.Abp.svg?style=flat-square)](https://docs.abp.io/en/abp/latest/Nightly-Builds)
 [![NuGet Download](https://img.shields.io/nuget/dt/Volo.Abp.Core.svg?style=flat-square)](https://www.nuget.org/packages/Volo.Abp.Core)
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+[![CLA Signed](https://cla-assistant.io/readme/badge/abpframework/abp)](https://cla-assistant.io/abpframework/abp)
 [![ABP Discord server](https://img.shields.io/discord/951497912645476422?label=Discord)](https://discord.gg/abp)
 
 ABP Framework is a complete **infrastructure** based on **ASP.NET Core** to create **modern web applications** and **APIs** by following the software development **best practices** and the **latest technologies**. Check out https://abp.io