Document the mechanics of "drawing the angle of attack" in the README…

…_android.md (#9341)

docs/README_android.md

@@ -34,6 +34,10 @@ performed (the cell/cells to be moved to, the angle of attack and the cells subj
 affected by this spell, potential damage, and so on). The second touch event is confirmatory, and performs the corresponding
 action if and only if this action exactly corresponds to the action that the first touch demonstrates.
 
+To make it easier to select the angle of attack on touchscreens, you can "draw" the angle by swiping your finger from the cell you
+intend to attack from, to the cell occupied by the enemy unit. Next, you should remove your finger from the screen, double-check
+your planned attack, and then confirm the action by touching the target cell with your finger again.
+
 ## Android specific notes
 Fullscreen is enabled by default. To have the info bar with the clock visible you can disable fullscreen mode within the
 main menu settings under "Graphics".