add doc

README.md

@@ -226,9 +226,9 @@ See [examples](examples).
 - [voxel/vx_from](https://openhome.cc/eGossip/OpenSCAD/lib2x-vx_from.html)
 - [voxel/vx_ascii](https://openhome.cc/eGossip/OpenSCAD/lib2x-vx_ascii.html)
 - [voxel/vx_gray](https://openhome.cc/eGossip/OpenSCAD/lib2x-vx_gray.html)
-- vx_union
-- vx_intersection
-- vx_difference
+- [voxel/vx_union](https://openhome.cc/eGossip/OpenSCAD/lib2x-vx_union.html)
+- voxel/vx_intersection
+- voxel/vx_difference
 
 ----
 

docs/lib2x-vx_union.md

@@ -0,0 +1,28 @@
+# vx_union
+
+Creates a union of two lists of points. 
+
+**Since:** 2.4
+
+## Parameters
+
+- `points1` : A list of points.
+- `points2` : A list of points.
+
+## Examples
+
+	use <voxel/vx_cylinder.scad>;
+	use <voxel/vx_sphere.scad>;
+	use <voxel/vx_union.scad>;
+
+	voxels = vx_union(
+		vx_cylinder([10, 15], 10),
+		vx_sphere(10)
+	);
+
+	for(pt = voxels) {
+		translate(pt)
+			cube(1, center = true);
+	}
+
+![vx_union](images/lib2x-vx_union-1.JPG)

src/voxel/vx_union.scad

@@ -1,3 +1,13 @@
+/**
+* vx_union.scad
+*
+* @copyright Justin Lin, 2020
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib2x-vx_union.html
+*
+**/ 
+
 use <../util/sort.scad>;
 use <../util/dedup.scad>;