Update the walkthrough and quick setting user documentation

docs/code-howtos/walkthrough.md

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+---
+parent: Code Howtos
+---
+
+# Walkthrough
+
+All walkthroughs are written using the internal declarative API (see `org.jabref.gui.walkthrough.declarative`) and are
+defined in the `WalkthroughAction` class. Each walkthrough is a linear series of steps, where each step is either a UI
+highlight (`VisibleComponent`) or an invisible side effect (`WalkthroughSideEffect`). The walkthroughs are built using a
+builder API (`Walkthrough.Builder`). To launch a walkthrough, simply construct a new `WalkthroughAction` and pass the
+name of the desired walkthrough.
+
+The `WalkthroughOverlay` renderer takes the output of the declarative API (`Walkthrough`) and renders it for the user.
+At a high level, a walkthrough primarily highlights GUI elements (nodes in the scene graph).
+
+The following step types are supported:
+
+## Highlights
+
+1. `Ring`: Shows a small, accent-colored circle in the upper-right corner of the node to be highlighted.
+   ![A blue, semi-transparent circle highlighting the "Preferences" button](../images/ring.png)
+2. `Spotlight`: Highlights the node of interest by darkening the rest of the window.
+   ![The "File" menu item highlighted with a spotlight effect](../images/backdrop.png)
+3. `FullScreenDarken`: Darkens the entire window, typically to display a panel in the center.
+   ![The entire application window darkened](../images/fullscreen-darken.png)
+
+## Visual Steps
+
+1. `TooltipStep`: Shows a tooltip next to a specified node. This step must be associated with a node to display
+   correctly.
+   ![A tooltip pointing to "Use Main File Directory"](../images/tooltip.png)
+2. `PanelStep`: Shows a panel with rich text and info boxes on the top, left, bottom, or right of the screen.
+   ![A information panel displayed at the top of the screen.](../images/panel-step.png)
+
+## Side Effects
+
+1. `OpenLibrarySideEffect`: Opens a specified example library.
+2. `EnsureSearchSettingsSideEffect`: Forces a search preference into a desired state.
+
+All walkthroughs are currently launched from the `Walkthroughs` component, which is located exclusively on the
+`WelcomeTab`.
+
+![The "Walkthroughs" section of the Welcome Tab, showing a list of available walkthroughs](../images/walkthroughs.png)
+
+## Quick Settings
+
+Since walkthroughs are only supposed to highlight UI components and guide the user through JabRef, quick settings are
+create so as to provide a convenient entry point for the user to edit the common settings like theme, online services,
+and main file directory. All the quick settings items are present in the `org.jabref.gui.welcome.components.QuickSettings`
+component, which is visible in the `WelcomeTab`.
+
+![The 'Quick Settings' section of the Welcome Tab, showing options for main file directory, theme, online settings, etc](../images/quicksettings.png)