documentation: add flatpak documentation

formatter.nix

@@ -13,6 +13,10 @@
         "pkgs/clan-vm-manager".extraPythonPackages =
           self'.packages.clan-vm-manager.externalTestDeps ++ self'.packages.clan-cli.testDependencies;
       };
+      treefmt.settings.formatter.mypy.excludes = [
+        "*/flatpak-builder"
+        "*/build-dir"
+      ];
 
       treefmt.settings.formatter.nix = {
         command = "sh";

pkgs/clan-cli/flatpak/FLATPAK.md

@@ -0,0 +1,21 @@
+# Flatpak Documentation
+
+
+## Installing locally
+
+You can install the package locally through `flatpak-builder`:
+```sh
+flatpak-builder --user --install --force-clean build-dir org.clan.cli.yml
+```
+
+## Debugging
+
+```sh
+flatpak run --devel --command=sh org.clan.cli
+```
+
+Replace `org.clan.cli` with the desired identifier.
+Now you can run commands inside the sandbox, for example:
+```sh
+[📦 org.clan.cli clan-cli-flatpak]$ strace -f -o strace.log clan vms run syncthing-peer1
+```