Update CONTRIBUTION.md with MEF error diagnostics

CONTRIBUTION.md

@@ -49,3 +49,9 @@ Starting Visual Studio every time to just check if a button is at a right positi
 * Once you have selected the proper run settings (see above), all tests should pass locally. The tests in the `Reqnroll.VisualStudio.Specs` might take longer for the first time, but they cache the necessary packages so for the subsequent runs they are fast.
 
 * Doing test-driven development might require to build the project regularly, but the installation of the package to the Visual Studio Experimental Instance takes quite much time. To overcome that, you can switch from the "Debug" configuration to "TestDebug" that does not compile the `Reqnroll.VisualStudio.Package` project by default. Since this project does only packaging and does not  contain testable logic, you can run the tests locally without building this project. Once you are ready to test it in Visual Studio Experimental Instance, you can build the `Reqnroll.VisualStudio.Package` project explicitly by invoking the "Build" command from the project node in solution explorer.
+
+## Diagnosing MEF Composition Errors
+
+Visual Studio and also our plugin uses [Managed Extensibility Framework (MEF)](https://learn.microsoft.com/en-us/dotnet/framework/mef/) for managing the dependencies. Unfortunately diagnosing MEF problems is hard, because the error messages are not very descriptive.
+
+For diagnosing MEF composition errors, you can check the [article by Daniel Plaisted](https://learn.microsoft.com/en-us/archive/blogs/dsplaisted/how-to-debug-and-diagnose-mef-failures) that contains a lot of useful ideas. Unfortunately we could not figure out how to enable logging in Visual Studio, but in case of any errors, **you should check the component cache error log file**. The file is a text file with name `Microsoft.VisualStudio.Default.err` and it is located in the `ComponentModelCache` folder of the Visual Studio user configuration folder. For the Visual Studio Experimental Instance, this is `C:\Users\<your-user>\AppData\Local\Microsoft\VisualStudio\17.0_921b0c10Exp\ComponentModelCache\Microsoft.VisualStudio.Default.err`. You can search for "Reqnroll" in this file and you might find information about the composition error causes the problems.