Can use libgit2 to add an unregistered submodule to index
tree3e6c4ccb9a86fc1d55cd3d6fc4a6a2a00ff23992
-rw-r--r-- 439 .gitignore
-rw-r--r-- 878 .gitmodules
-rw-r--r-- 224 .mailmap
-rw-r--r-- 231 .tgitconfig
drwxr-xr-x - Languages
-rw-r--r-- 3843 README.md
-rw-r--r-- 1040 appveyor.yml
-rw-r--r-- 6137 architecture.txt
-rw-r--r-- 2615 build.txt
drwxr-xr-x - contrib
drwxr-xr-x - doc
drwxr-xr-x - ext
-rw-r--r-- 952 release.txt
drwxr-xr-x - src
drwxr-xr-x - test