How to access app.config file in class library type project?

I have created Add-In project for outlook in .Net 3.5 using Shared Add In project.
This project downloads attachments from selected mail in outlook and save it in our database.

I want to store connection string for Sql Server and physical path to the folder where I want to download all attachments.

I want to put this information in App.config file so user can change it according to his/her requirement and configuration.

I tried to add this information in app.config file but I can not fetch stored information.

I think that app.config file not working because my project is class library type.

How can I use app.config file or is there any other alternate to getting same job?