add doc

README.md

@@ -208,6 +208,9 @@ See [examples](examples).
 
 ### Util
 - [util/sum](https://openhome.cc/eGossip/OpenSCAD/lib2x-sum.html)
+- [util/zip](https://openhome.cc/eGossip/OpenSCAD/lib2x-zip.html)
+
+----
 
 ## Bugs and Feedback
 

docs/lib2x-zip.md

@@ -0,0 +1,19 @@
+# zip
+
+Make a list that aggregates elements from each of the lists. Returns a list of lists, where the i-th list contains the i-th element from each of the argument lists. The `zip` function stops when the first input list is exhausted. 
+
+**Since:** 2.4
+
+## Parameters
+
+- `lts` : a list of lists.
+
+## Examples
+
+    use <util/zip.scad>;
+
+    xs = [10, 20, 30];
+    ys = [5, 15, 25];
+    zs = [2.5, 7.5, 12.4];
+
+    assert(zip([xs, ys, zs]) == [[10, 5, 2.5], [20, 15, 7.5], [30, 25, 12.4]]);

src/util/zip.scad

@@ -1,3 +1,13 @@
+/**
+* zip.scad
+*
+* @copyright Justin Lin, 2020
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib2x-zip.html
+*
+**/ 
+
 use <_impl/_zip_impl.scad>;
 
-function zip(lists) = _zipAll(lists);
+function zip(lts) = _zipAll(lts);