Add documentation

docs/workflow.md

@@ -84,4 +84,9 @@ Note that any changes to model fields, field ordering, or factories, will likely
 
 It is possible that a PR has Percy-flagged changes, despite the PR not touching model/factory code nor introducing changes to the front-end code. In this case, please alert the engineering team: we've seen this happen in the past and it is unclear why it happens.
 
+Because we have run into the need to check visual regression manually pretty quickly after adding the above, you can also trigger visual regression tests by adding the label `run visual regression tests` to the PR.
+The **adding** is the trigger.
+So if you want to run the tests again, just remove and re-add the label.
+The PR approval trigger will also still run the regression tests.
+
 For more information on how to work with visual regression tests, see the [Percy docs](https://docs.percy.io/docs).