Place the cursor on the first line you wish to have the revision bar.
Then have a look at Page Layout > Page Backgound > Page Borders.
Select the Borders (first) tab.
This will allow you to create a vertical bar similar to what you would do in formatting a table.
Note: If you select multiple lines, make sure that Paragraph is selected in the Apply to combo box.
Once created you can select the bar (click and hold) and drag it left or right.