added keynote.md and updated SwiftUI.md

Author: mvolkmann

src/content/topics/keynote.md

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+---
+eleventyNavigation:
+  key: Keynote
+layout: topic-layout.njk
+---
+
+## Overview
+
+This page documents selected features of the macOS app Keynote
+for creating slide presentations.
+It is far from comprehensive.
+
+## Build Effects
+
+Build effects gradually display the contents of a slide.
+For example, in a slide with bullet points,
+text boxes, and shapes (such as arrows),
+you may wish to display the bullets one at a time and
+display the text boxes and arrows when a specific bullet is appears.
+To do this:
+
+1. For each set of text boxes and shapes that should appear together ...
+   1. Select each item in the set.
+   1. Click the animation button (contains two overlapping diamonds)
+      in the upper-right to show animation options.
+   1. Click the "Add an Effect" button.
+   1. Select "Appear".
+
+1. Select the single set of bullets.
+1. Click the animation button.
+1. Click the "Add an Effect" button.
+1. Select "Appear".
+1. Change the "Deliver" dropdown value to "By Bullet" or "By Bullet Group".
+1. Click the "Build Order" button at the bottom of the panel.
+1. For each non-bullet item ...
+   1. Drag it to below the bullet after which it should appear.
+   1. Change its "Start" dropdown value to "With Build n" or "After Build n".
+
+1. Optionally click the "Preview" button to see how
+   all the items on the slide will animate into view.
+
+"With Build" means that multiple items begin their animation at the same time.
+"After Build" means that the animation of that item
+begins after the animation of the preceding item.
+When the effect is "Appear", the animation is instantaneous,
+so there is no visible difference between "With Build" and "After Build".