Multi-cargo ships: Sprite group cargo thresholds refer to entire ship

docs/newgrf-additions-nml.html

@@ -83,6 +83,8 @@
 		The default graphics chain for the primary vehicle may check the cargo states of the other ship parts if required.<br />
 		Additional ship parts may be refitted individually.
 		<p>This requires the <span class="code">multi_part_ships</span> feature.</p>
+
+		<p>From version 3 of the <span class="code">multi_part_ships</span> feature, spritegroup loading/loaded cargo thresholds refer to the entire ship, not just the first vehicle.</p>
 	</p>
 	<p>
 		Added callback: <span class="code">refit_part_name</span><br />