Add a tab to the credits panel for mod-specific text.

Enabled by adding a ModCredits block to mod.yaml.

OpenRA.Mods.Common/ModCredits.cs

@@ -0,0 +1,21 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2018 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+namespace OpenRA
+{
+	public class ModCredits : IGlobalModData
+	{
+		public readonly string ModTabTitle = "Game";
+
+		[FieldLoader.Require]
+		public readonly string ModCreditsFile = null;
+	}
+}