The question is not very clearly formulated, but I guess you need the documentation of your code to appear in Visual Studio Intellisense (which is not really auto-complete but some more advanced functionality).
You are looking in wrong direction: attributes are designed for very different purposes. The attributes can affect run-time behavior through Reflection, but you don't want to contaminate your code with something which is only needed during development, through Visual Studio or not. Therefore, Visual Studio supports completely different mechanism called XML Documentation Comments.
The idea is this: you comment some of your types and members with special comments which works like regular comments from the standpoint of C# but are processed in a special way by Visual Studio. Such comments are recognized by special comment delimiters:
or
As you can see, in this way C# recognized such markup as comments. Start typing "///" one the line before a type or a member to be documented, and Visual Studio will create a minimalistic comment template for you.
Inside such comments, you can write specially formatted XML documentation to denote methods, parameters, cross-references, etc.
Please see:
http://msdn.microsoft.com/en-us/library/b2s063f7.aspx[
^].
It creates the documentation in a special file which is, by default, is created and used only for Debug configuration, but you can change it in the project properties — please see the tab "Build", "XML Documentation file".
Enjoy,
—SA