adding rfc implemented in listcommands

doc/rfc_documents.txt

@@ -21,6 +21,9 @@ RFC 2195   IMAP/POP AUTHorize Extension for Simple Challenge/Response
 RFC 2221   IMAP4 Login Referrals
 RFC 2298   Details return receipts
 RFC 2342   The IMAP4 NAMESPACE command
+RFC 2369   The Use of URLs as Meta-Syntax for Core Mail List Commands and their
+           Transport through Message Header Fields 
+           (implemented in listcommands plugin)
 RFC 2616   HTTP/1.1
 RFC 2683   IMAP4 Implementation Recommendations
 RFC 2822   Format of an email message (sendmail)