cmd/tailscale: fix command descriptions (#1710)

Signed-off-by: Ross Zurowski <ross@rosszurowski.com>

cmd/tailscale/cli/logout.go

@@ -16,7 +16,7 @@ import (
 var logoutCmd = &ffcli.Command{
 	Name:       "logout",
 	ShortUsage: "logout [flags]",
-	ShortHelp:  "down + expire current node key",
+	ShortHelp:  "Disconnect from Tailscale and expire current node key",
 
 	LongHelp: strings.TrimSpace(`
 "tailscale logout" brings the network down and invalidates

cmd/tailscale/cli/up.go

@@ -30,7 +30,7 @@ import (
 var upCmd = &ffcli.Command{
 	Name:       "up",
 	ShortUsage: "up [flags]",
-	ShortHelp:  "Connect to your Tailscale network",
+	ShortHelp:  "Connect to Tailscale, logging in if needed",
 
 	LongHelp: strings.TrimSpace(`
 "tailscale up" connects this machine to your Tailscale network,