Add alt text to logo

Add alt text to .NET Foundation logo to resolve MD045 warning.

README.md

@@ -2,7 +2,7 @@
 
 Polly is a .NET resilience and transient-fault-handling library that allows developers to express resilience strategies such as Retry, Circuit Breaker, Hedging, Timeout, Rate Limiter and Fallback in a fluent and thread-safe manner.
 
-[<img align="right" src="https://github.com/dotnet/swag/raw/main/logo/dotnetfoundation_v4_small.png" width="100" />](https://www.dotnetfoundation.org/)
+[<img align="right" src="https://github.com/dotnet/swag/raw/main/logo/dotnetfoundation_v4_small.png" width="100" alt="The .NET Foundation logo" />](https://www.dotnetfoundation.org/)
 We are a member of the [.NET Foundation](https://www.dotnetfoundation.org/about)!
 
 **Keep up to date with new feature announcements, tips & tricks, and other news through [www.thepollyproject.org](https://www.thepollyproject.org)**