reference to a commit that isn't already in the local submodule
clone.
+-j::
+--jobs=<n>::
+ Number of parallel children to be used for fetching submodules.
+ Each will fetch from different submodules, such that fetching many
+ submodules will be faster. By default submodules will be fetched
+ one at a time.
+
--no-recurse-submodules::
Disable recursive fetching of submodules (this has the same effect as
using the '--recurse-submodules=no' option).