To add submodule
-Create new repository. ex "submodule-child"
-Initiate just like normal repo
-cd submodule-parent
-clone submodule-child --> submodule-child
-Enable Git submodule summary -> git config --global status.submoduleSummary true
-git status -> submodule exist
-git commit -m "- Add submodule"
-git push --> add submodule to submodule-parent