Add xmldoc to some ISpriteFrame members

OpenRA.Game/Graphics/SpriteLoader.cs

@@ -24,8 +24,17 @@ namespace OpenRA.Graphics
 
 	public interface ISpriteFrame
 	{
+		/// <summary>
+		/// Size of the frame's `Data`.
+		/// </summary>
 		Size Size { get; }
+
+		/// <summary>
+		/// Size of the entire frame including the frame's `Size`.
+		/// Think of this like a picture frame.
+		/// </summary>
 		Size FrameSize { get; }
+
 		float2 Offset { get; }
 		byte[] Data { get; }
 		bool DisableExportPadding { get; }