To add markup to a project plan while adding to a post, click into the post and tap + More from the bottom-right corner. Choose Drawing Markup and navigate to the appropriate drawing.
You can pan and zoom to find the appropriate placement and then choose from the available tools at the bottom of the drawing. You can add clouds, shapes, lines, arrows as well as use a pencil or highlighter marker.
You can also add text to your drawing. Type directly on the drawing, resize and position the text exactly where you want it, and choose what color it appears, if you'd like.
Your plan markup will not be on the actual drawing itself, but a snapshot of it that will be included with the post. You can add as many snapshots from as many different drawings as you need.
Note: Adding markup to an already posted post is only available on mobile devices.