add doc

README.md

@@ -243,6 +243,10 @@ These examples incubate dotSCAD and dotSCAD refactors these examples. See [examp
 - [bauer_spiral](https://openhome.cc/eGossip/OpenSCAD/lib2x-bauer_spiral.html)
 - [fibonacci_lattice](https://openhome.cc/eGossip/OpenSCAD/lib2x-fibonacci_lattice.html)
 
+### Util
+
+- [lerp](https://openhome.cc/eGossip/OpenSCAD/lib2x-lerp.html)
+
 ### Voxel
 
 - [vx_bezier](https://openhome.cc/eGossip/OpenSCAD/lib2x-vx_bezier.html)

docs/lib2x-lerp.md

@@ -0,0 +1,17 @@
+# lerp
+
+Linear interpolate the vector v1 to v2.
+
+**Since:** 2.5
+
+## Parameters
+
+- `v1` : Minimum value of random number range. Default to 0.
+- `v2` : Maximum value of random number range. Default to 1.
+- `amt` : The amount of interpolation. Some value between 0.0 and 1.0.
+
+## Examples
+
+    use <util/lerp.scad>;
+    
+    assert(lerp([0, 0, 0], [100, 100, 100], 0.5) == [50, 50, 50]);  

src/util/lerp.scad

@@ -1,3 +1,13 @@
+/**
+* lerp.scad
+*
+* @copyright Justin Lin, 2020
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib2x-lerp.html
+*
+**/ 
+
 function lerp(v1, v2, amt) = 
     let(
         v = v2 - v1,