add "--recurse-submodules=no" to downlaod / git fetch commands hint

If you work on qtmodule which contains submodules like qtwebenigne, and your change includes updated sha for submodule which is not yet reviewed and not merged the "download" commands will not work. It will end up in error message "not our ref". This is due to the fact that indeed 3rparty sha is not in local clone as it is still on gerrit. However adding --recurse-submodules=no to fetch command solves the issue and it does not hurt to have it (have no real impact on changes in repositories which do not have submodules)

This is quite common scenario for qtwebenigne module where changes in submodule have to be tested beforehand on ci , and there is no other way than having update commit in parent repo.

Please note It would be helpful for people who are not aware of the issue and just want to copy paste command from gerrit "download"

For time being you can try to checkout https://codereview.qt-project.org/c/qt/qtwebengine/+/609739 to see the issue for yourself