git submodules are great, they allow you to add another repository to an existing project. So that you can keep your dependencies separate and managed by separate repos.
It's great fo decoupling code where it makes sense.
Adding submodule to an existing project
Change directory into the already GIT enabled project that you want to include a sub module into.
Run the submodule add command
This will initialise the submodule int you existing project.
Run git status
You will notice a new file called
.gitmodules in your project. This file will list all submodules initialised.