message: Update doc for submodules
diff: @@ -33,6 +33,9 @@ Hera, used for Wasserstein distance, is available on an external git repository.
  git submodule update --init
  ```
  +[gudhi-deploy](https://github.com/GUDHI/gudhi-deploy) is used for Continuous Integration python
  +requirements and will also be downloaded by the above command.
  +
  ## Configuring a remote for a fork
  ```bash
  git remote add upstream https://github.com/GUDHI/gudhi-devel.git
  