+add::
+ Add the given repository as a submodule at the given path
+ to the changeset to be committed next. In particular, the
+ repository is cloned at the specified path, added to the
+ changeset and registered in .gitmodules. If no path is
+ specified, the path is deduced from the repository specification.
+ If the repository url begins with ./ or ../, it is stored as
+ given but resolved as a relative path from the main project's
+ url when cloning.
+