You can attach javadocs to a library via "File -> Project Structure". Then under "Modules" click on "Dependencies" where you'll see a list of libraries used by the project (provided you've added some before). Choose a library, click on"Edit...", and you'll get a dialog where you can attach the javadocs to it.
I"m talking about configuring the default javadoc elements that occur when we create a new class or an interface. Where do I set the author name, version and since attributes for all classes that gets created through idea?