add doc

docs/lib2x-vx_difference.md

@@ -0,0 +1,28 @@
+# vx_difference
+
+It' slow, in case you want to create a difference of two lists of points directly. 
+
+**Since:** 2.4
+
+## Parameters
+
+- `points1` : A list of points.
+- `points2` : A list of points.
+
+## Examples
+
+	use <voxel/vx_difference.scad>;
+	use <voxel/vx_cylinder.scad>;
+	use <voxel/vx_sphere.scad>;
+
+	voxels = vx_difference(
+		vx_cylinder(6, 3, filled = true),
+		vx_sphere(3, filled = true)
+	);
+
+	for(pt = voxels) {
+		translate(pt)
+			cube(1, center = true);
+	}
+
+![vx_difference](images/lib2x-vx_difference-1.JPG)

docs/lib2x-vx_intersection.md

@@ -1,6 +1,6 @@
 # vx_intersection
 
-Creates an intersection of two lists of points. 
+It' slow, in case you want to create an intersection of two lists of points directly. 
 
 **Since:** 2.4
 

docs/lib2x-vx_union.md

@@ -1,6 +1,6 @@
 # vx_union
 
-Creates a union of two lists of points. 
+It' slow, in case you want to create a union of two lists of points directly. 
 
 **Since:** 2.4