doc: document http.IncomingMessage behaviour change

Add to the history table that the `destroyed` value returns `true` after
the incoming data is consumed.

Refs: #36617
Refs: #33035

PR-URL: #36641
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>

doc/api/http.md

@@ -1892,6 +1892,10 @@ the request body should be sent.
 <!-- YAML
 added: v0.1.17
 changes:
+  - version: v15.5.0
+    pr-url: https://github.com/nodejs/node/pull/33035
+    description: The `destroyed` value returns `true` after the incoming data
+                 is consumed.
   - version:
      - v13.1.0
      - v12.16.0
@@ -1906,6 +1910,11 @@ An `IncomingMessage` object is created by [`http.Server`][] or
 and [`'response'`][] event respectively. It may be used to access response
 status, headers and data.
 
+Different from it's `socket` value which is a subclass of {stream.Duplex}, the
+`IncomingMessage` itself extends {stream.Readable} and is created separately to
+parse and emit the incoming HTTP headers and payload, as the underlying socket
+may be reused multiple times in case of keep-alive.
+
 ### Event: `'aborted'`
 <!-- YAML
 added: v0.3.8