I'm positive that this guide existed, but my Google skills seem to be broken today. Could you show me the link to the MSDN pointing to that section?
It's called "Design Guidelines for Developing Class Libraries" and can be found here in the MSDN
First link in google after pasting in your question:
http://msdn.microsoft.com/en-us/library/aa720433%28VS.71%29.aspx
Is this what you are looking for?
Design Guidelines for Class Library Developers
As you figured out yourself, the article you were originally looking for is called Design Guidelines for Developing Class Libraries on the MSDN.
Note that it also exists a great complete book on the very same topic, named Framework Design Guidelines. Actually, the MSDN page encourages you to have a look at this book if you want to go deeper:
For more information on design guidelines, see the "Framework Design Guidelines: Conventions, Idioms, and Patterns for Reusable .NET Libraries" book by Krzysztof Cwalina and Brad Abrams, published by Addison-Wesley, 2005.