Update flatpak.md

Author: lwindolf

Cheat Sheets/Packaging/flatpak.md

@@ -9,3 +9,15 @@
     flatpak uninstall --unused
 
     flatpak run <package>
+
+## Debugging
+
+Enter package environment with a shell:
+
+    flatpak install --include-debug <package>
+    flatpak install --include-sdk <package>
+    flatpak run --command=sh --devel --filesystem=$(pwd) <package<
+
+In the started shell you can start the flatpak'ed binary with gdb for example.
+
+See also https://docs.flatpak.org/en/latest/debugging.html