Add the draw.io app to your Google browser from the google store. Alternately, you can go directly to www.draw.io to use the app.
Once you launch the app, scroll down to Entity Relation in the left side window and click on it. You will see all the symbols needed to draw your ERD. Simply drag and drop the symbols on your page, then edit as needed.
Export your drawing in .png format (or another format of your choice) so that you can easily insert it in your solution document.
Note: When saving/exporting, your document will be stored in your local Downloads folder.