Allow users to use both username and email address (if unique) for site login.
Step 1. Login as an administrator and select Administration
Step 2. Select Site Administration
Step 3. Select Plugins tab
Step 4. Find Admin tools section
Step 5. Select Manage Authentication
Step 6. Find Allow login via email
Step 7. Check the Allow login via email checkbox to enable this feature.
Step 8. Scroll to the bottom of the screen and select Save Changes
This feature has now been enabled and will add / email address as part of the description on the login page.