Tutorial improvement - Belt merging mechanics

[vvv444]

Just some feedback... For me as a new player it wasn't obvious that belts can be merged (side loading from one belt to another). Until I opened the forum I merged belts with inserters which is quite bulky, I strongly propose to add that to tutorial or in-game tips.
Actually, it is shown in the "Two sides of belts" tip, but I would add a sentence about it to draw players attention.