The draw.io Google Docs Add-on is an extension to Google Docs that allows draw.io diagrams to be easily inserted and updated within Google Docs.
If you haven't already installed draw.io to your Drive, go to drive.draw.io and create your first diagram. Once that diagram is saved in your Google Drive, you'll be able to import it to your Google Doc using this Add-on.
For more details on how to select Google Drive as the storage mechanism at the draw.io web site, see Using draw.io with Google Drive.
To install the draw.io Add-on for Google Docs, go to the Chrome Web Store entry, then click on the "+FREE" button at the right top of the draw.io listing
Accept the permissions that appear to install draw.io. In terms of the permissions, we don't have any control of what is requested. We don't need anything other than the ability to read your draw.io diagrams, the requested scope are considerably wider than we would prefer, currently.
To create a diagram, go to drive.google.com, click Create and select a draw.io diagram, or create a non-realtime diagram or a realtime diagram directly.
To insert an existing draw.io diagram, navigate to Add-ons -> Draw.io Diagram -> Insert Diagram.
This will bring up your Google Drive file picker
Select the file you wish to insert and once loaded you will see an image of the diagram embedded in your document.
Updating your Diagram(s)
To update one or more diagrams in your document, if the diagrams have been updated in the draw.io application, either select the diagram to update and go to Draw.io Diagrams -> Update Selected
Or to update all diagrams in the document invoke Draw.io Diagrams -> Update All.