doc: add note on tls connection meta data methods

DaftMonk · Fishrock123 · commit 597f8751d179 · 2015-11-11T12:11:16.000-05:00
PR-URL: #3746 Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
diff --git a/doc/api/tls.markdown b/doc/api/tls.markdown
@@ -764,6 +764,10 @@ of written data and all required TLS negotiation.
 This instance implements a duplex [Stream][] interfaces.  It has all the
 common stream methods and events.
 
+Methods that return TLS connection meta data (e.g.
+[getPeerCertificate](#tlssocketgetpeercertificate-detailed-))
+will only return data while the connection is open.
+
 ### Event: 'secureConnect'
 
 This event is emitted after a new connection has been successfully handshaked.
