Add indications to subcommands in the console

[Katolus]

To make it clear to people using the --help options that some of the commands have subtypes.

[Katolus]

# Commands that have subcommands
Groups:
   gcp     Deploy functions in GCP
  new     Factory method for creating new functions
...

# Commands that don't have a subcommand
Commands:
  add     Adds a function to the registry
  build   Builds an image of a given function
  config  Renders function's configuration file into the command line
  delete  Delete a function from the registry
  error   A command for testing error messages
  list    List existing functions
  remove  Removes a local image of a functions
  run     Start a container for a given function
  stop    Stops a running function
  sync    Sync components