VMM/cli: Activated help subcommand.
Implemented Command.help_(), which reads the command's help message from
cli.clihelp.
# All parameters are described in pgsql_table(5) / PGSQL PARAMETERS
#
# The hosts that Postfix will try to connect to and query from.
hosts = localhost
# The user name and password to log into the pgsql server.
user = postfix
password = some_password
# The database name on the servers.
dbname = mailsys
# The SQL query template used to search the database
query = SELECT maildir FROM postfix_virtual_mailbox_map('%u', '%d')