doc/how-to: Add doc explanation of filter restriction

Signed-off-by: Max Asnaashari <[email protected]>

doc/how-to/preseed.yaml

@@ -77,6 +77,7 @@ ovn:
   dns_servers: 192.0.2.1,2001:db8:d:200::1
 
 # `storage` is optional and is used as basic filtering logic for finding disks across all systems.
+# Filters will only apply to systems which do not have an explicitly defined disk above for the corresponding storage type.
 # Filters are checked in order of appearance.
 # The names and values of each key correspond to the YAML field names for the `api.ResouresStorageDisk`
 # struct here: