cmd: add tlsinfo.

cmd/tlsinfo/README.txt

@@ -0,0 +1,34 @@
+tlsinfo: show TLS version, cipher, and peer certificates
+---------------------------------------------------------
+
+Description
+  tlsinfo connects to a TLS server and prints the negotiated TLS version and
+  cipher suite, followed by details for each certificate in the server’s
+  presented chain (as provided by the server).
+
+Usage
+  tlsinfo <hostname:port>
+
+Output
+  The program prints the negotiated protocol and cipher, then one section per
+  certificate in the order received from the server. Example fields:
+    TLS Version: TLS 1.3
+    Cipher Suite: TLS_AES_128_GCM_SHA256
+    Certificate 1
+        Subject: CN=example.com, O=Example Corp, C=US
+        Issuer: CN=Example Root CA, O=Example Corp, C=US
+        DNS Names: [example.com www.example.com]
+        Not Before: 2025-01-01 00:00:00 +0000 UTC
+        Not After:  2026-01-01 23:59:59 +0000 UTC
+
+Examples
+  # Inspect a public HTTPS endpoint
+  tlsinfo example.com:443
+
+Notes
+  - Verification is intentionally disabled (InsecureSkipVerify=true). The tool
+    does not validate the server certificate or hostname; it is for inspection
+    only.
+  - The SNI/ServerName is inferred from <hostname> when applicable.
+  - You must specify a port (e.g., 443 for HTTPS).
+  - The entire certificate chain is printed exactly as presented by the server.