Add comment to export test to help understand the test failure (#78182)

## Description
I ran into an issue with test that was very easy to resolve once I
understood the issue, adding a comment block incase someone runs into
this in the future so they can get a general sense of the issue and next
steps.

tests/sentry/backup/test_exports.py

@@ -380,6 +380,16 @@ def test_export_filter_orgs_multiple(self):
             assert not self.exists(data, OrganizationMember, "user_email", "user_b_only")
             assert not self.exists(data, OrganizationMember, "email", "invited-b@example.com")
 
+    """
+    If this test fails, it's because a newly created model was given an relocation_scope
+    that is not correctly exporting the models created in backup.py
+
+    To fix this you can:
+    - Add a reference to the organization model
+    - Remove the model from the relocation scope; using RelocationScope.Excluded
+    - Reach out to #discuss-open-source on slack for customizations / more detailed support
+    """
+
     def test_export_filter_orgs_empty(self):
         a = self.create_exhaustive_user("user_a_only")
         b = self.create_exhaustive_user("user_b_only")