docs: Add sketch-on-face docs page (#7924)

* docs: Add sketch-on-face docs page

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: jtran

docs/kcl-lang/sketch-on-face.md

@@ -0,0 +1,90 @@
+---
+title: "Sketch on Face"
+excerpt: "Sketching on the face of a solid using the KCL language for the Zoo Design Studio."
+layout: manual
+---
+
+When you sketch on a plane and extrude, a new solid is created.
+
+```kcl
+cube = startSketchOn(XY)
+  |> startProfile(at = [0, 0])
+  |> line(end = [1, 0])
+  |> line(end = [0, 1])
+  |> line(end = [-1, 0])
+  |> line(end = [0, -1])
+  |> close()
+  |> extrude(length = 1)
+```
+
+However, when you sketch on the face of an existing solid, extruding extends the
+existing solid.
+
+```kcl
+cube = startSketchOn(XY)
+  |> startProfile(at = [0, 0])
+  |> line(end = [1, 0])
+  |> line(end = [0, 1])
+  |> line(end = [-1, 0])
+  |> line(end = [0, -1])
+  |> close()
+  |> extrude(length = 1)
+
+tower = startSketchOn(cube, face = END)
+  |> circle(center = [0.5, 0.5], diameter = 0.2)
+  |> extrude(length = 0.8)
+```
+
+The result is that there's only one solid. You can think about this as being
+equivalent to making a new, separate solid and unioning the two in a single
+operation.
+
+On the other hand, if you don't want to change the initial solid and create a
+new solid instead, there are a couple ways to do this.
+
+The first way is instead of starting the sketch on the face of the solid, start
+the sketch on the same plane. Since it's not directly on the first solid's face,
+extrusions do not modify the solid. They create new solids instead.
+
+```kcl
+cube = startSketchOn(XY)
+  |> startProfile(at = [0, 0])
+  |> line(end = [1, 0])
+  |> line(end = [0, 1])
+  |> line(end = [-1, 0])
+  |> line(end = [0, -1])
+  |> close()
+  |> extrude(length = 1)
+
+// This tower is a separate solid from the cube.
+tower = startSketchOn(planeOf(cube, face = END))
+  |> circle(center = [0.5, 0.5], diameter = 0.2)
+  |> extrude(length = 0.8)
+```
+
+The second way to create a separate solid is by using the `method` parameter of
+`extrude()`. You can start the sketch on the face, but when extruding, specify
+that the method should create a new solid using `method = NEW`.
+
+```kcl
+cube = startSketchOn(XY)
+  |> startProfile(at = [0, 0])
+  |> line(end = [1, 0])
+  |> line(end = [0, 1])
+  |> line(end = [-1, 0])
+  |> line(end = [0, -1])
+  |> close()
+  |> extrude(length = 1)
+
+// This tower is a separate solid from the cube.
+tower = startSketchOn(cube, face = END)
+  |> circle(center = [0.5, 0.5], diameter = 0.2)
+  |> extrude(method = NEW, length = 0.8)
+```
+
+Once you have a separate solid, you can translate or rotate it separately or use
+boolean operations like union, subtract, and intersect.
+
+If you intend to create a single solid, you should prefer to sketch-on-face
+since it's more succinct, efficient, and robust. But sometimes you need the
+flexibility of creating a separate solid.

docs/kcl-std/functions/std-sketch-extrude.md

@@ -25,6 +25,11 @@ extrude(
 You can provide more than one sketch to extrude, and they will all be
 extruded in the same direction.
 
+When you sketch on a face of a solid, extruding extends or cuts into the
+existing solid, meaning you don't need to union or subtract the volumes. You
+can change this behavior by using the `method` parameter. See
+[sketch on face](/docs/kcl-lang/sketch-on-face) for more details.
+
 ### Arguments
 
 | Name | Type | Description | Required |

docs/kcl-std/functions/std-sketch-startSketchOn.md

@@ -34,6 +34,8 @@ The point is if you want to export the result of a sketch on a face, you
 only need to export the final Solid that was created from the sketch on the
 face, since it will include all the parent faces and Solids.
 
+See [sketch on face](/docs/kcl-lang/sketch-on-face) for more details.
+
 ### Arguments
 
 | Name | Type | Description | Required |

e2e/playwright/snapshot-tests.spec.ts-snapshots/Draft-segments-should-look-right-3-Google-Chrome-linux.png

@@ -26,6 +26,7 @@
 /// only need to export the final Solid that was created from the sketch on the
 /// face, since it will include all the parent faces and Solids.
 ///
+/// See [sketch on face](/docs/kcl-lang/sketch-on-face) for more details.
 ///
 /// ```kcl
 /// exampleSketch = startSketchOn(XY)
@@ -376,6 +377,11 @@ export fn ellipse(
 /// You can provide more than one sketch to extrude, and they will all be
 /// extruded in the same direction.
 ///
+/// When you sketch on a face of a solid, extruding extends or cuts into the
+/// existing solid, meaning you don't need to union or subtract the volumes. You
+/// can change this behavior by using the `method` parameter. See
+/// [sketch on face](/docs/kcl-lang/sketch-on-face) for more details.
+///
 /// ```kcl
 /// example = startSketchOn(XZ)
 ///   |> startProfile(at = [0, 0])