Yep it is not very straightforward. Hopefully the controls aren't that complex but still, I think you're right it needs explanation. During the game jam I thought of adding a few lines and images to show the controls (on the right/left of the screen) but I didn't have time to do it (I've barely had time to make the webGL build after instlling another version of unity, because the one I was using was crashing every time I tried to buid).