Make the function signature less prominent, add an early example to docs

Signed-off-by: Nick Cameron <nrc@ncameron.org>

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

@@ -8,11 +8,17 @@ layout: manual
 Compute the length of the provided line segment.
 
 ```kcl
-segLen(@tag: TaggedEdge): number(Length)
+exampleSketch = startSketchOn(XZ)
+  |> startProfile(at = [0, 0])
+  |> angledLine(angle = 60, length = 10, tag = $thing)
+  |> tangentialArc(angle = -120deg, radius = 5)
+  |> angledLine(angle = -60deg, length = segLen(thing))
+  |> close()
+
+example = extrude(exampleSketch, length = 5)
+
 ```
 
-
-
 ### Arguments
 
 | Name | Type | Description | Required |
@@ -24,6 +30,12 @@ segLen(@tag: TaggedEdge): number(Length)
 [`number(Length)`](/docs/kcl-std/types/std-types-number) - A number.
 
 
+### Function signature
+
+```kcl
+segLen(@tag: TaggedEdge): number(Length)
+```
+
 ### Examples
 
 ```kcl