Add doc note about STARTTLS

doc/api/tls.markdown

@@ -51,6 +51,19 @@ signed by one of the specified CAs. If `s.authorized === false` then the error
 can be found in `s.authorizationError`.
 
 
+### STARTTLS
+
+In the v0.4 branch no function exists for starting a TLS session on an
+already existing TCP connection.  This is possible it just requires a bit of
+work. The technique is to use `tls.createSecurePair()` which returns two
+streams: an encrypted stream and a plaintext stream. The encrypted stream is then
+piped to the socket, the plaintext stream is what the user interacts with thereafter.
+
+[Here is some code that does it.](http://gist.github.com/848444)
+
+
+
+
 ### tls.Server
 
 This class is a subclass of `net.Server` and has the same methods on it.