Submodules
From charlesreid1
To clone a repo plus all of its submodules (not done by default!), use the recursive flag:
git clone --recursive <git-repo-address>
If you forgot to use the recursive flag, initialize all the submodules from the repo folder via:
git submodule update --init
If you have all the submodules and you want to update all of them from their respective remotes, use
git submodule update --remote