flatpak --user install flathub - a fix

docs/devs/building/qt-desktop-gui.md

@@ -55,7 +55,7 @@ make USE_UPNP=yes
 ```
 sudo apt install flatpak flatpak-builder
 flatpak --user remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
-flatpak --user install org.kde.Sdk/x86_64/5.11     # required SDK version might be higher, recheck the manifest 
+flatpak --user install flathub org.kde.Sdk/x86_64/5.11     # required SDK version might be higher, recheck the manifest 
 git clone https://github.com/flathub/website.i2pd.i2pd && cd website.i2pd.i2pd 
 flatpak-builder --user --install --force-clean i2pd_build_dir website.i2pd.i2pd.json
 ```