Editorial: clarify why "webidentity" is not part of RequestDestination

Author: annevk

fetch.bs

@@ -1557,6 +1557,8 @@ the empty string,
 "<code>worker</code>", or
 "<code>xslt</code>". Unless stated otherwise it is the empty string.
 
+<p class=note>These are reflected on {{RequestDestination}} except for "<code>serviceworker</code>"
+and "<code>webidentity</code>" as fetches with those destinations skip service workers.
 <!-- Dependencies:
      * CSP: https://w3c.github.io/webappsec-csp/#effective-directive-for-a-request
      * Mixed Content
@@ -8499,6 +8501,7 @@ Nikki Bee,
 Nikunj Mehta,
 Noam Rosenthal,
 Odin Hørthe Omdal,
+Olli Pettay,
 Ondřej Žára,
 O. Opsec,
 Perry Jiang<!-- perryjiang; Github -->,