Update mstest0010.md (dotnet#41913)

* Update mstest0010.md

* Update mstest0010.md

Author: engyebrahim

docs/core/testing/mstest-analyzers/mstest0010.md

@@ -39,6 +39,7 @@ Methods marked with `[ClassInitialize]` should follow the following layout to be
 - it should not be generic
 - it should take one parameter of type `TestContext`
 - return type should be `void`, `Task` or `ValueTask`
+- `InheritanceBehavior.BeforeEachDerivedClass` attribute parameter should be specified if the class is `abstract`.
 
 [!INCLUDE [test-class-rules](includes/test-class-rules.md)]