Reference HTTP WG style guide (#587)

As this will include a bunch of useful guidance in working with HTTP in
specifications that we don't need to maintain.

Closes #422.

Author: martinthomson

index.bs

@@ -529,8 +529,9 @@ An incomplete list of such guidance follows:
 * [[encoding#specification-hooks|Encoding]]
 * [[fetch#fetch-elsewhere|Fetch]]
 * <span id="using-http">[[RFC9205 inline]]</span>,
-    especially on [[RFC9205#section-4.7|defining header fields]], and
-    [other HTTP RFCs](https://datatracker.ietf.org/doc/search?name=HTTP&amp;sort=&amp;rfcs=on&amp;by=group&amp;group=httpbis)
+    especially on [[RFC9205#section-4.7|defining header fields]],
+    [other HTTP RFCs](https://datatracker.ietf.org/doc/search?name=HTTP&amp;sort=&amp;rfcs=on&amp;by=group&amp;group=httpbis),
+    and the [HTTP Working Group style guide](https://httpwg.org/admin/editors/style-guide)
 * [[hr-time#sec-tools|Time]]
 * [[url#url-apis-elsewhere|URLs]]