Merge branch 'wk/submodule-on-branch'

Make sure 'submodule update' modes that do not detach HEADs can be used more pleasantly by checking out a concrete branch when cloning them to prime the well. * wk/submodule-on-branch: Documentation: describe 'submodule update --remote' use case submodule: explicit local branch creation in module_clone submodule: document module_clone arguments in comments submodule: make 'checkout' update_module mode more explicit