End Credits: added explanatory label regarding speed controls

data/gui/window/end_credits.cfg

@@ -47,6 +47,11 @@
 
 		{GUI_WINDOW_FULLSCREEN}
 
+		[linked_group]
+			id = "helptext"
+			fixed_width = "true"
+		[/linked_group]
+
 		[tooltip]
 			id = "tooltip"
 		[/tooltip]
@@ -73,7 +78,19 @@
 
 							[row]
 
+								# Reserve the same amount of space on the left so the middle column is centererd
 								[column]
+									grow_factor = 0
+
+									[spacer]
+										definition = "default"
+										linked_group = "helptext"
+									[/spacer]
+
+								[/column]
+
+								[column]
+									grow_factor = 1
 									horizontal_grow = "true"
 									vertical_grow = "true"
 
@@ -87,6 +104,21 @@
 
 								[/column]
 
+								[column]
+									grow_factor = 0
+									horizontal_alignment = "right"
+									vertical_alignment = "bottom"
+									border = "all"
+									border_size = 5
+
+									[label]
+										definition = "default"
+										label = _ "↑ ↓ to adjust speed"
+										linked_group = "helptext"
+									[/label]
+
+								[/column]
+
 							[/row]
 
 						[/grid]