cmd/tailscale/cli: fix inconsistency between serve text and example command

Use the same local port number in both, and be more precise about what
is being forwarded

Signed-off-by: Mihai Parparita <mihai@tailscale.com>

cmd/tailscale/cli/serve.go

@@ -66,10 +66,12 @@ EXAMPLES
   - To serve simple static text:
     $ tailscale serve https:8080 / text:"Hello, world!"
 
-  - To forward raw TCP packets to a local TCP server on port 5432:
+  - To forward incoming TCP connections on port 2222 to a local TCP server on
+    port 22 (e.g. to run OpenSSH in parallel with Tailscale SSH):
     $ tailscale serve tcp:2222 tcp://localhost:22
 
-  - To forward raw, TLS-terminated TCP packets to a local TCP server on port 80:
+  - To accept TCP TLS connections (terminated within tailscaled) proxied to a
+    local plaintext server on port 80:
     $ tailscale serve tls-terminated-tcp:443 tcp://localhost:80
 `),
 		Exec:      e.runServe,