Add current submodule HEAD commit to index of superproject.
@param submodule The submodule to add to the index
@param write_index Boolean if this should immediately write the index
file. If you pass this as false, you will have to get the
git_index and explicitly call git_index_write() on it to
save the change.
@return 0 on success, <0 on failure
Add current submodule HEAD commit to index of superproject.
@param submodule The submodule to add to the index @param write_index Boolean if this should immediately write the index file. If you pass this as false, you will have to get the git_index and explicitly call git_index_write() on it to save the change. @return 0 on success, <0 on failure