Fix desktop launch, app icons and keyboard parameter editing

docs/book/src/guide/getting-started.md

@@ -19,6 +19,31 @@ cargo run --release -p solvecraft -- --sample   # opens with a sample part
 `solvecraft design.solvecraft` opens a saved design. Windows builds cross-compile from Linux with
 `cargo xwin build --release --target x86_64-pc-windows-msvc -p solvecraft`.
 
+### Linux Flatpak
+
+Install Flatpak using your distribution's package manager. For an installation that receives
+updates, add Flathub for the required Freedesktop runtime and the SolidCraft application feed
+to the same user installation:
+
+```sh
+flatpak remote-add --user --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo
+flatpak remote-add --user --if-not-exists solvecraft https://bherbruck.github.io/solidcraft/flatpak/solvecraft.flatpakrepo
+flatpak install --user solvecraft ai.storyteller.solvecraft
+flatpak run ai.storyteller.solvecraft
+```
+
+The application ID and remote name retain their compatibility names. To update an existing
+remote that still uses the former website address, run
+`flatpak remote-modify --user --url=https://bherbruck.github.io/solidcraft/flatpak/repo/ solvecraft`
+and then `flatpak update --user`.
+
+Alternatively, download the release's `.flatpak` file for your architecture and run
+`flatpak install --user ./solvecraft-VERSION-linux-ARCH.flatpak`. The bundle supplies the
+Flathub runtime repository address; installation still needs internet access to fetch any
+missing runtime. Launch with `flatpak run ai.storyteller.solvecraft`, rather than looking for
+a host `solvecraft` binary. Files chosen through Open/Save use the desktop file-chooser portal;
+command-line paths outside Documents may need a specific additional filesystem permission.
+
 ## Web
 
 The same app runs in the browser: [open SolidCraft on the web](../app/) (`?sample` opens the sample