message: Mention git submodule sync
diff: @@ -25,10 +25,10 @@ This creates a directory gudhi-devel, which you are free to move around or renam
  cd gudhi-devel
  ```
  -Everytime you clone the repository, you will have to download the *submodules*.
  +When you clone the repository, you also need to download the *submodules*.
  ## Submodules
  -An interface to Hera for Wasserstein distance is available on an external git repository. To download it:
  +Hera, used for Wasserstein distance, is available on an external git repository. To download it:
  ```bash
  git submodule update --init
  ```
  @@ -60,8 +60,9 @@ 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:
  +**Reminder:** If the version of a submodule has changed, or if a submodule was added, you may need to:
  ```bash
  +git submodule sync
  git submodule update --init
  ```
  