git subtree add --prefix lib/OpenBLAS https://github.com/xianyi/OpenBLAS master --squash
git log
git subtree pull --prefix lib/OpenBLAS https://github.com/xianyi/OpenBLAS master --squash
tricky and slow
subtree repository has no knowledge of the original repository.
Is the external repository something you own yourself and are likely to push code back to? submodule (dont forget to run a git submodule update.)
Is the external repository third party code that you are unlikely to push anything back to? subtree