cmd/inspect: add help

cmd/inspect/inspect.go

@@ -26,10 +26,20 @@ var (
 // Register the "inspect" subcommand.
 func Register(root *cobra.Command) {
 	cmd := &cobra.Command{
-		Use:   "inspect",
+		Use:   "inspect source [source2 …]",
 		Short: "Inspect files and TLS servers",
-		RunE:  Inspect,
-		Args:  cobra.MinimumNArgs(1),
+		Long: `Allows inspection of RSA keys, X.509 certificates, CRLs and CSRs. Pass
+it a list of sources. Valid sources are:
+ • filenames
+ • ‘-’ for stdin
+ • host:port for extracting the server's certificate chain from a TLS handshake
+ • https://addr.example/ as per host:port
+
+The output will by default be human-readable formatted text for the terminal,
+but JSON and YAML are also supported through the --output flag.`,
+
+		RunE: Inspect,
+		Args: cobra.MinimumNArgs(1),
 	}
 
 	if isatty.IsTerminal(1) {