https://andrey.nering.com.br/2016/git-submodules-vs-subtrees/

====== submodules ======
Submodule is only a link to commit ref in another repo.

=== Add ===
Adding submodule:
<code bash>
git submodule add <repository> [<relative_local_path>]
</code>

=== Init ===
After cloning master repo with submodules:
<code bash>
git submodule init
git submodule update
</code>

alternatively repo can be clonned with 
<code bash>
git clone --recursive <url>
</code>


<code bash>
git submodule update --init --recursive
git fetch --recurse-submodules
</code>




=== Remove ===

Removing submodule:
  * <code bash>git submodule deinit lib/lib_to_be_deleted</code>
  * remove entry in ''.gitmodules''
  * stage ''.gitmodules''
  * ? remove entry in ''.git/config''
  * remove dir: ''git rm --cached lib/lib_to_be_deleted''
  * remove module content: ''rm -rf .git/modules/lib_to_be_deleted''