Git submodules

Add repo as submodule:

git add submodule git@github.com:user/repo-sub.git ~/path/to/subdir/

Clone repo with submodules:

git clone --recurse-submodules git@github.com:user/repo.git

Pull submodules into local repo:

git submodule update --init --recursive

Update submodules:

git submodule update --remote --merge