# add a new submodule to an existing git repository
git submodule add <url.git> dir
git submodule init

# clone a git repository inclusive its submodules
git clone --recursive <url.git>

# pull changes from parent and submodules
git pull --recurse-submodules

# push changes to parent and submodules
git push --recurse-submodules=on-demand

# pull all changes from parent and submodules
git pull --recurse-submodules

# got into submodule directory
cd plugins/greetings-de

# make some changes, e.g. add a comment
...

# stage and commit changes, as you would usually do
git add .
git commit -m"made some changes"

# go back to the main repository
cd ..

# let parent reference the new changes, by adding them in a new commit
git add .
git commit -m"updated submodule"

# publish all changes
git push --recurse-submodules=on-demand