doc(cli): restore help text for helm configuration

Signed-off-by: Marc Khouzam <marc.khouzam@ville.montreal.qc.ca>

cmd/helm/root.go

@@ -121,6 +121,22 @@ Environment:
   $HELM_DRIVER        set the backend storage driver. Values are: configmap, secret, memory
   $HELM_NO_PLUGINS    disable plugins. Set HELM_NO_PLUGINS=1 to disable plugins.
   $KUBECONFIG         set an alternative Kubernetes configuration file (default "~/.kube/config")
+
+Helm stores configuration based on the XDG base directory specification, so
+
+- cached files are stored in $XDG_CACHE_HOME/helm
+- configuration is stored in $XDG_CONFIG_HOME/helm
+- data is stored in $XDG_DATA_HOME/helm
+
+By default, the default directories depend on the Operating System. The defaults are listed below:
+
++------------------+---------------------------+--------------------------------+-------------------------+
+| Operating System | Cache Path                | Configuration Path             | Data Path               |
++------------------+---------------------------+--------------------------------+-------------------------+
+| Linux            | $HOME/.cache/helm         | $HOME/.config/helm             | $HOME/.local/share/helm |
+| macOS            | $HOME/Library/Caches/helm | $HOME/Library/Preferences/helm | $HOME/Library/helm      |
+| Windows          | %TEMP%\helm               | %APPDATA%\helm                 | %APPDATA%\helm          |
++------------------+---------------------------+--------------------------------+-------------------------+
 `
 
 func newRootCmd(actionConfig *action.Configuration, out io.Writer, args []string) *cobra.Command {