Update README.md

Adding CI badge

Author: gowon

README.md

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 A [SecureStore](https://github.com/neosmart/SecureStore) configuration provider to use with .NET Core's `Microsoft.Extensions.Configuration`.
 
+![build](https://github.com/gowon/SecureStore.Contrib.Configuration/workflows/build/badge.svg)
+
 ### Installing 
 
 Install using the [SecureStore.Contrib.Configuration package](https://www.nuget.org/packages/SecureStore.Contrib.Configuration):
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 ## License
 
-MIT
+MIT