Sometimes you have Drupal in a git repository and you want to use a single submodule from Luggage. For example, you might have a site on which you want only the People feature.
Here is how to add a submodule to your git repository.
In English, you are telling your git repository that contains the code for your website where the git submodule is, so that when you type
git submodule update --init
it will automatically pull in the submodule.
First, you add the submodule by hand:
git submodule add firstname.lastname@example.org:isubit/luggage_people.git sites/all/modules/luggage/luggage_people
This has updated the .gitmodules file in your repository. So now you should commit the changed .gitmodules file to your repository, so next time you clone the repository it will contain the pointer to the submodule
git add .gitmodules sites/all/modules/luggage/luggage_people.
commit -m 'Adding people as a submodule'