add docs

docs/lib2x-nz_perlin1.md

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+# nz_perlin1
+
+Returns the 1D [Perlin noise](https://en.wikipedia.org/wiki/Perlin_noise) value at the x coordinate.
+
+**Since:** 2.3
+
+## Parameters
+
+- `x` : The x coordinate.
+- `seed` : The random seed.
+
+## Examples
+
+    use <hull_polyline2d.scad>;
+    use <util/rand.scad>;
+    use <noise/nz_perlin1.scad>;
+
+    seed = rand();
+    hull_polyline2d(
+        [for(x = [0:.1:10]) [x, nz_perlin1(x, seed)]], width = .1
+    );
+
+![nz_perlin1](images/lib2x-nz_perlin1-1.JPG)

docs/lib2x-nz_perlin1s.md

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+# nz_perlin1s
+
+Returns 1D [Perlin noise](https://en.wikipedia.org/wiki/Perlin_noise) values at x coordinates.
+
+**Since:** 2.3
+
+## Parameters
+
+- `xs` : The x coordinate.
+- `seed` : The random seed. If it's ignored, a randomized value will be used.
+
+## Examples
+
+    use <hull_polyline2d.scad>;
+    use <noise/nz_perlin1s.scad>;
+
+    xs = [for(x = [0:.1:10]) x];
+    ys = nz_perlin1s(xs);
+    points = [for(i = [0:len(xs) - 1]) [xs[i], ys[i]]];
+
+    hull_polyline2d(points, width = .1);
+
+![nz_perlin1s](images/lib2x-nz_perlin1s-1.JPG)