dh(chore): Added usefeedbacks documentation

docs/apps/datahub.md

@@ -4,6 +4,13 @@ outline: deep
 
 # Datahub
 
+## Pre-requesite
+
+### Useefeedbacks
+The user feedbacks section will not work with geonetwork 4.2.2 if you don't set a proper mail configuration:
+
+In the legacy geonetwork-ui, log as admin, then go in "Admin console" and select "Settings", then add a proper value in the "SMTP host" field e.g. `[email protected]` (it doesn't need to be a real SMTP server but it has to be a valid adress) then click on the "Save settings" button in the top right corner of that page and now the userfeedbacks should work.
+
 ## Metadata pages
 
 Each metadata has its own detailed page, made of multiple sections, described as followed.