RFC6265bis: Add case insensitivity note to Set-Cookie Syntax (#2167)

* Add case insensitivity note to Set-Cookie Syntax

* Remove incorrect parenthetical

Co-authored-by: sbingler <bingler@chromium.org>

draft-ietf-httpbis-rfc6265bis.md

@@ -522,6 +522,10 @@ Note that some of the grammatical terms above reference documents that use
 different grammatical notations than this document (which uses ABNF from
 {{RFC5234}}).
 
+NOTE: The name of an attribute-value pair is not case sensitive. So while they
+are presented here in CamelCase, such as "HttpOnly" or "SameSite", any case is
+accepted. E.x.: "httponly", "Httponly", "hTTPoNLY", etc.
+
 The semantics of the cookie-value are not defined by this document.
 
 To maximize compatibility with user agents, servers that wish to store arbitrary