doc,http2: add parameters for Http2Session:connect event

Add parameters for the callback for the Http2Session:connect event
inline with the pattern in the rest of the documentation.

Refs: nodejs/help#877 (comment)

Author: ryzokuken

doc/api/http2.md

@@ -136,6 +136,9 @@ listener does not expect any arguments.
 added: v8.4.0
 -->
 
+* `session` {Http2Session}
+* `socket` {net.Socket}
+
 The `'connect'` event is emitted once the `Http2Session` has been successfully
 connected to the remote peer and communication may begin.