cmd/config: provide better help for configuration

Signed-off-by: Robin Hahling <robin.hahling@gw-computing.net>

cmd/config/config.go

@@ -24,7 +24,24 @@ func New(vp *viper.Viper) *cobra.Command {
 	configCmd := &cobra.Command{
 		Use:   "config",
 		Short: "Modify or view hubble config",
-		Long:  "Modify or view hubble config",
+		Long: `Config allows to modify or view the hubble configuration. Global hubble options
+can be set via flags, environment variables or a configuration file. The
+following precedence order is used:
+
+1. Flag
+2. Environment variable
+3. Configuration file
+4. Default value
+
+The "config view" subcommand provides a merged view of the configuration. The
+"config set" and "config reset" subcommand modify values in the configuration
+file.
+
+Environment variable names start with HUBBLE_ followed by the flag name
+capitalized where eventual dashes ('-') are replaced by underscores ('_').
+For example, the environment variable that corresponds to the "--server" flag
+is HUBBLE_SERVER. The environment variable for "--tls-allow-insecure" is
+HUBBLE_TLS_ALLOW_INSECURE and so on.`,
 		PersistentPreRunE: func(_ *cobra.Command, _ []string) error {
 			// override root persistent pre-run to avoid flag/config checks
 			// as we want to be able to modify/view the config even if it is