tailscale ping: note that `-c` can take 0 for infinity

Signed-off-by: Graham Christensen <graham@grahamc.com>

cmd/tailscale/cli/ping.go

@@ -51,7 +51,7 @@ relay node.
 		fs.BoolVar(&pingArgs.tsmp, "tsmp", false, "do a TSMP-level ping (through WireGuard, but not either host OS stack)")
 		fs.BoolVar(&pingArgs.icmp, "icmp", false, "do a ICMP-level ping (through WireGuard, but not the local host OS stack)")
 		fs.BoolVar(&pingArgs.peerAPI, "peerapi", false, "try hitting the peer's peerapi HTTP server")
-		fs.IntVar(&pingArgs.num, "c", 10, "max number of pings to send")
+		fs.IntVar(&pingArgs.num, "c", 10, "max number of pings to send. 0 for infinity.")
 		fs.DurationVar(&pingArgs.timeout, "timeout", 5*time.Second, "timeout before giving up on a ping")
 		return fs
 	})(),