Add link to certification poster

README.md

@@ -62,6 +62,9 @@ Corrections for typos and other mistakes and improvements like refactoring code.
 - [Improvements & Errata - list of corrections](docs/errata)
 - [Seventh edition's support for .NET 8](docs/dotnet8.md)
 
+## Microsoft Certifications
+Microsoft used to have exams and certifications for developers that covered skills like C# and ASP.NET. Sadly, they have retired them all. These days, the only developer-adjacent exams and certifications are for Azure or Power Platform, as you can see from the certification poster: https://aka.ms/traincertposter
+
 ## Microsoft .NET community support
 - [.NET Developer Community](https://dotnet.microsoft.com/platform/community)
 - [.NET Tech Community Forums for topic discussions](https://techcommunity.microsoft.com/t5/net/ct-p/dotnet)