Add example to CallerArgumentExpressionAttribute

The documentation for [CallerArgumentExpressionAttribute](https://docs.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.callerargumentexpressionattribute?view=net-6.0) should contain an example. Or at least it should link to https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/attributes/caller-information#argument-expressions were you can find some examples.