Document adding md-manuscript to the XFCE menu

Add an XFCE section to the install guide covering Whisker Menu
favourites (right-click → Add to Favorites), panel/desktop launcher
alternatives, and menu-refresh commands. Fold XFCE equivalents into the
on-screen keyboard, HiDPI, and X11 tips, and add a troubleshooting row.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

INSTALL-debian12-surface.md

@@ -1,7 +1,9 @@
 # Installing md-manuscript on a Surface tablet (Debian 12 "Bookworm")
 
 These steps build the app from source and set it up for touch use on a Microsoft
-Surface running Debian 12 with the GNOME desktop. You do **not** need the
+Surface running Debian 12. They assume the **GNOME** desktop, with **XFCE**
+equivalents called out where they differ (see *[Add md-manuscript to the XFCE
+menu](#add-md-manuscript-to-the-xfce-menu)*). You do **not** need the
 `linux-surface` custom kernel for this app — any working Debian 12 desktop is
 fine.
 
@@ -85,8 +87,9 @@ hardware. The result is `~/md-manuscript/target/release/md-manuscript`.
 
 ## 4. Install the binary and a launcher
 
-Put the binary on your `PATH` and add a GNOME app entry so it appears in the
+Put the binary on your `PATH` and add a desktop app entry so it appears in your
-Activities/app grid and can be pinned to the dash (handy for touch):
+applications menu (GNOME app grid / XFCE Whisker Menu) and can be pinned for
+touch:
 
 ```sh
 # 4a. Binary
@@ -121,6 +124,49 @@ You can now launch **md-manuscript** by tapping its icon, or run
 
 ---
 
+## Add md-manuscript to the XFCE menu
+
+XFCE reads the same `~/.local/share/applications/md-manuscript.desktop` launcher
+from step 4, so the app already appears under **Office** in the applications
+menu. To pin it as a favourite:
+
+**Whisker Menu (Favourites).** The Favourites feature lives in the *Whisker
+Menu* (the modern XFCE menu), not the classic *Applications Menu* plugin. Open
+the Whisker Menu, type `md-manuscript` (or find it under *Office*), then
+**right-click it → "Add to Favorites."** It moves to the Favourites column at the
+top-left of the menu, where you can right-click to reorder or remove it.
+
+If your panel still has the classic *Applications Menu* (which has no
+favourites), install and switch to Whisker:
+
+```sh
+sudo apt install -y xfce4-whiskermenu-plugin
+```
+
+then right-click the panel → *Panel → Add New Items… → Whisker Menu* (and remove
+the old menu plugin).
+
+**Panel launcher (alternative).** To place it directly on the panel: right-click
+the panel → *Panel → Add New Items… → Launcher → Add*, then right-click the new
+launcher → *Properties*, press **＋**, and pick **md-manuscript** from the list.
+
+**Desktop icon (alternative).** Copy the launcher onto the desktop:
+
+```sh
+cp ~/.local/share/applications/md-manuscript.desktop ~/Desktop/
+```
+
+(right-click it → *Allow Launching* the first time, if prompted).
+
+If it doesn't show up in the menu, refresh the database and restart the panel:
+
+```sh
+update-desktop-database ~/.local/share/applications 2>/dev/null || true
+xfce4-panel -r
+```
+
+---
+
 ## 5. First run
 
 1. In the top bar, set **Workspace** (default `~/Manuscript`) and tap **Open** —
@@ -143,15 +189,19 @@ You can now launch **md-manuscript** by tapping its icon, or run
 ## Surface-specific tips
 
 **On-screen keyboard (detached from Type Cover).**
-GNOME Settings → *Accessibility* → *Typing* → turn on **Screen Keyboard**. It
+GNOME Settings → *Accessibility* → *Typing* → turn on **Screen Keyboard**; it
-pops up automatically when you tap a text field. For terminal-heavy setup you may
+pops up automatically when you tap a text field. XFCE has no built-in one — install
-find it easier to attach the keyboard for the one-time install.
+`onboard` (`sudo apt install -y onboard`) and start it manually. For a
+terminal-heavy setup you may find it easier to attach the keyboard for the
+one-time install.
 
 **HiDPI / tiny or huge UI.**
 Surface screens are very high resolution. The app follows the desktop's scale
 factor, so set it once in GNOME Settings → *Displays* → **Scale** (enable
-*Fractional Scaling* if you want values like 150%/175%). If you run under X11 and
+*Fractional Scaling* if you want values like 150%/175%). On XFCE, use *Settings →
-the size is still off, launch with an explicit factor:
+Appearance → Fonts → Custom DPI* and/or *Settings → Display*, or raise `Xft/DPI`
+in *Settings Editor*. Because XFCE runs on X11, you can also launch with an
+explicit factor (this works on GNOME-under-X11 too):
 ```sh
 WINIT_X11_SCALE_FACTOR=1.75 md-manuscript
 ```
@@ -168,6 +218,8 @@ login screen, or force X11 for one launch:
 ```sh
 WINIT_UNIX_BACKEND=x11 md-manuscript
 ```
+XFCE is X11-only on Debian 12, so there is no Wayland toggle to worry about and
+the `WINIT_X11_SCALE_FACTOR` variable above applies directly.
 
 ---
 
@@ -199,5 +251,6 @@ rm -f ~/.local/share/applications/md-manuscript.desktop
 | **📂 Browse** buttons do nothing / no dialog appears | Install `xdg-desktop-portal` and `xdg-desktop-portal-gtk` (step 1b); you can still type paths by hand. |
 | Build error mentioning `rustc … is not supported` | `rustup update`, then `cargo build --release` again. |
 | `cargo: command not found` | Run `. "$HOME/.cargo/env"` or open a new terminal after installing rustup. |
-| UI text far too small/large | Adjust GNOME *Displays → Scale*, or set `WINIT_X11_SCALE_FACTOR` (X11). |
+| UI text far too small/large | Adjust GNOME *Displays → Scale* (or XFCE *Appearance → Fonts → Custom DPI*), or set `WINIT_X11_SCALE_FACTOR` (X11). |
+| Not in the XFCE menu / no **Add to Favorites** | Run `update-desktop-database ~/.local/share/applications` and `xfce4-panel -r`; favourites need the *Whisker Menu* (`xfce4-whiskermenu-plugin`), not the classic Applications Menu. |
 | **⟳ Sync** does nothing / errors in the Log panel | Set `git config --global user.name/user.email`, and ensure the `origin` remote and your SSH/HTTPS credentials are configured. |