improve kbd docs (#1707)

* improve kbd docs

Author: cscheid

docs/authoring/_kbd.qmd

@@ -1,6 +1,12 @@
 {{< include ../_require-1.3.qmd >}}
 
-The `kbd` [shortcode](shortcodes.qmd) can be used to describe keyboard shortcuts in documentation. On Javascript formats, it will attempt to detect the operating system of the format and show the correct shortcut. On print formats, it will print the keyboard shortcut information for all operating systems.
+The `kbd` [shortcode](shortcodes.qmd) can be used to describe keyboard shortcuts in documentation:
+
+- single keyboard shortcuts for every operating system use a **positional parameter**: `{{{< kbd Ctrl-C >}}}`
+- different shortcuts for different operating systems use **keyword parameters `win`, `mac`, and `linux`**: `{{{< kbd mac=Shift-Command-O win=Shift-Control-O linux=Shift-Ctrl-L >}}}`
+
+On Javascript formats, Quarto will attempt to detect the operating system of the format and show the correct shortcut.
+On print formats, it will print the keyboard shortcut information for all operating systems.
 
 For example, writing the following markdown: