stats: add docs

Signed-off-by: Akihiro Suda <[email protected]>

README.md

@@ -939,9 +939,16 @@ Flags:
 ### :whale: nerdctl stats
 Display a live stream of container(s) resource usage statistics.
 
+NOTE: no support for network I/O on cgroup v2 hosts (yet), see issue [#516](https://github.com/containerd/nerdctl/issues/516)
 
 Usage: `nerdctl stats [flags]`
 
+Flags:
+- :whale: `-a, --all`: Show all containers (default shows just running)
+- :whale: `--format=FORMAT`: Pretty-print images using a Go template, e.g., `{{json .}}`
+- :whale: `--no-stream`: Disable streaming stats and only pull the first result
+- :whale: `--no-trunc `: Do not truncate output
+
 ### :whale: nerdctl top
 Display the running processes of a container.
 

cmd/nerdctl/stats.go

@@ -44,9 +44,12 @@ import (
 )
 
 func newStatsCommand() *cobra.Command {
+	short := "Display a live stream of container(s) resource usage statistics."
+	long := short + "\nNOTE: no support for network I/O on cgroup v2 hosts (yet), see https://github.com/containerd/nerdctl/issues/516"
 	var statsCommand = &cobra.Command{
 		Use:               "stats",
-		Short:             "Display a live stream of container(s) resource usage statistics.",
+		Short:             short,
+		Long:              long,
 		RunE:              statsAction,
 		ValidArgsFunction: statsShellComplete,
 		SilenceUsage:      true,
@@ -60,7 +63,7 @@ func newStatsCommand() *cobra.Command {
 
 func addStatsFlags(cmd *cobra.Command) {
 	cmd.Flags().BoolP("all", "a", false, "Show all containers (default shows just running)")
-	cmd.Flags().String("format", "", "Pretty-print images using a Go template")
+	cmd.Flags().String("format", "", "Pretty-print images using a Go template, e.g, '{{json .}}'")
 	cmd.Flags().Bool("no-stream", false, "Disable streaming stats and only pull the first result")
 	cmd.Flags().Bool("no-trunc", false, "Do not truncate output")
 }