Add project files.

AlientAttack.MonoGame/Things/MoveableSprite.cs

@@ -0,0 +1,15 @@
+namespace AlienAttack.MonoGame.Things;
+
+public class MoveableSprite(int x, int y) : Sprite(x, y)
+{
+    public float XVelocity { get; protected set; } = 0;
+    public float YVelocity { get; protected set; } = 0;
+
+    public override void Update(SpriteUpdateContext context)
+    {
+        XPosition += XVelocity;
+        YPosition += YVelocity;
+
+        base.Update(context);
+    }
+}