checkout the commit specified in the index of the containing repository.
This will make the submodules HEAD be detached unless `--rebase` or
`--merge` is specified or the key `submodule.$name.update` is set to
- `rebase`, `merge` or `none`. `none` can be overriden by specifying
+ `rebase`, `merge` or `none`. `none` can be overridden by specifying
`--checkout`.
+
If the submodule is not yet initialized, and you just want to use the