mention the '-o -' trick

docs/curl.1

@@ -863,7 +863,8 @@ or use several variables like:
 You may use this option as many times as the number of URLs you have.
 
 See also the \fI--create-dirs\fP option to create the local directories
-dynamically.
+dynamically. Specifying the output as '-' (a single dash) will force the
+output to be done to stdout.
 .IP "-O/--remote-name"
 Write output to a local file named like the remote file we get. (Only the file
 part of the remote file is used, the path is cut off.)