updated README

Author: jlallemand

README.md

@@ -17,7 +17,7 @@ which provides e.g. Debian packets for the latest pandoc.
 To populate and update the submodule, run:
 ```
 git submodule init
-git submodule update
+git submodule update --remote
 ```
 
 <!> Jsquirrel compilation requires to uninstall why3. The doc compilation requires to have why3 installed...