Add doc about init_groups command in README

2 jobs for 7-gestion-des-droits-utilisateur-code-interface in 2 minutes and 32 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Test
passed unit tests #3094
preprod

00:00:59

83.0%
 
  Build
passed static build #3095
preprod

00:01:33