doc: clarify response.finished

PR-URL: #28411
Refs: jshttp/on-finished#30
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

doc/api/http.md

@@ -1172,8 +1172,8 @@ added: v0.0.2
 
 * {boolean}
 
-Boolean value that indicates whether the response has completed. Starts
-as `false`. After [`response.end()`][] executes, the value will be `true`.
+The `response.finished` property will be `true` if [`response.end()`][]
+has been called.
 
 ### response.getHeader(name)
 <!-- YAML