Add Token type specification to RateLimit field section

Co-authored-by: darrelmiller <[email protected]>

Author: Copilot

draft-ietf-httpapi-ratelimit-headers.md

@@ -227,7 +227,7 @@ The following example shows a policy with a partition key and a quota unit:
 
 A server uses the "RateLimit" response header field to communicate the current service limit for a quota policy for a particular partition key.
 
-The field is expressed as a List{{SF}} of Service Limit Items ({{servicelimit-item}}).
+The field is expressed as a List{{SF}} of Service Limit Items ({{servicelimit-item}}). The Item{{SF}} value MUST be a Token{{SF}}.
 
 Lists of Service Limit Items can be split over multiple "RateLimit" fields in the same HTTP response as described in {{Section 3.1 of SF}}.