Google has added the option for teachers to add materials like digital handouts to the Classwork section in Google Classroom. Judging by the emails and Tweets I've already seen, this is going to be a popular feature. To help you get started adding materials to your Google Classroom Classwork section, I made the following tutorial video.
Applications for Education
The option to add materials to Google Classroom without having to post an assignment or question is a feature that teachers have been asking for since Google rolled-out the new version of Google Classroom. This update should make it easier for you to distribute materials like videos, documents, slides, and audio files as handouts under the topics in the Classwork section in your Google Classroom classes.