add groups section in the getting started guide.
Suggest to prefer configuration with env vars instead of modifying
the default configuration file
Signed-off-by: Nicola Murino <nicola.murino@gmail.com>
Using groups simplifies the administration of multiple accounts by
letting you assign settings once to a group, instead of multiple
times to each individual user.
Signed-off-by: Nicola Murino <nicola.murino@gmail.com>
