* Added a couple others

doc/rfc_documents.txt

@@ -13,6 +13,8 @@ NUMBER     DESCRIPTION
 RFC 822    Format of an email message (sendmail)
 RFC 1730   IMAP version 4
 RFC 2060   IMAP version 4rev1
+RFC 2183   Content-Disposition MIME header
 RFC 2298   Details return receipts
 RFC 2342   The IMAP4 NAMESPACE command
+RFC 2616   HTTP/1.1
 RFC 2683   IMAP4 Implementation Recommendations