Google docs can be incorporated into your Groupsite by using a shareable link to the doc. Here are two options for sharing the Google doc link with your group's members.
1. Use a Shared Link module to post links to the Google docs. You can share up to 15 links in one module. If the Google doc link in the module renders a blank page and not the document text, review the Google "Share" settings on the document. You may have to make adjustments to the Share settings so that your Groupsite members can view the document.
2. Add a page to the "More" tab using the "External Page" format. The document link is added to the More page and the More subtab for that page becomes a link directly to the document; one More subtab per document. Again, you may need to adjust the Share settings.