message: Doc review: submodule rephrase [skip ci]
diff: @@ -25,9 +25,10 @@ This creates a directory gudhi-devel, which you are free to move around or renam
  cd gudhi-devel
  ```
  -## Submodule
  -An interface to Hera for Wasserstein distance is available on an external git repository.
  -Everytime you checkout master or merge from master, afterwards, you will need to run the command:
  +Everytime you clone the repository, you will have to download the *submodules*.
  +
  +## Submodules
  +An interface to Hera for Wasserstein distance is available on an external git repository. To download it:
  ```bash
  git submodule update --init
  ```
  @@ -59,6 +60,11 @@ This is a command you can run quite regularly.
  It tells git to check all that happened on github.
  It is safe, it will not mess with your files.
  +**Reminder:** Everytime you checkout master or merge from master, afterwards, if the version of one the submodule has changed, or if a submodule was added, you will have to:
  +```bash
  +git submodule update --init
  +```
  +
  ## Create a branch, based on the current master
  ```bash
  git checkout -b some-fancy-name --no-track upstream/master
  