show a user friendly description of the starting unit template

closes #6209

OpenRA.Mods.RA/MPStartUnits.cs

@@ -15,10 +15,19 @@ namespace OpenRA.Mods.RA
 	[Desc("Used by SpawnMPUnits. Attach these to the world actor. You can have multiple variants by adding @suffixes.")]
 	public class MPStartUnitsInfo : TraitInfo<MPStartUnits>
 	{
+		[Desc("Internal class ID.")]
 		public readonly string Class = "none";
+
+		[Desc("Exposed via the UI to the player.")]
+		public readonly string ClassName = "Unlabeled";
+
+		[Desc("Only available when selecting this faction.", "Leave empty for no restrictions.")]
 		public readonly string[] Races = { };
 
+		[Desc("The mobile construction vehicle.")]
 		public readonly string BaseActor = null;
+
+		[Desc("A group of units ready to defend or scout.")]
 		public readonly string[] SupportActors = { };
 
 		[Desc("Inner radius for spawning support actors")]