add doc

README.md

@@ -371,7 +371,7 @@ These examples incubate dotSCAD and dotSCAD refactors these examples. See [examp
 --|--
 [**select**(i)](https://openhome.cc/eGossip/OpenSCAD/lib3x-select.html) | select module objects.
 [**polyline_join**(points)](https://openhome.cc/eGossip/OpenSCAD/lib3x-polyline_join.html) | place a join on each point. Hull each pair of joins and union all convex hulls.
-shape_star | create a 2D star.
+[**shape_star**([outer_radius, inner_radius, n])](https://openhome.cc/eGossip/OpenSCAD/lib3x-shape_star.html) | create a 2D star.
 
 ## Polyhedra
 

docs/lib3x-star.md

@@ -0,0 +1,22 @@
+# shape_star 
+
+Create a star. Default to a pentagram.
+
+**Since:** 3.2
+
+## Parameters
+
+- `outer_radius`: the outer radius of the star. Default to 1.
+- `inner_radius`: the inner radius of the star. Default to 0.381966.
+- `n`: the burst number. Default to 5.
+
+## Examples
+
+	use <shape_star.scad>;
+
+	polygon(shape_star());
+	translate([3, 0, 0]) 
+	    polygon(shape_star(n = 8));
+
+![shape_star](images/lib3x-shape_star-1.JPG)
+

src/shape_star.scad

@@ -10,4 +10,4 @@
 
 use <_impl/_shape_star_impl.scad>;
 
-function shape_star(outerRadius = 1, innerRadius = 0.381966, n = 5) = _shape_star_impl(outerRadius, innerRadius, n);
+function shape_star(outer_radius = 1, inner_radius = 0.381966, n = 5) = _shape_star_impl(outer_radius, inner_radius, n);