Rework the README after the second review

The nine findings: the heap figure keeps the old README's meaning; the
Makefile sentence names the three targets that call no script; the five
fields /api/v1/stats adds are a list; the test comment names README
"JSON API"; the X-Forwarded-For readers are a list, with short sentences
after it; the AS page's peers are the ASes next to it in AS paths; CIDR
ranges and the default route are explained; handle and description are
field names; the TODO entry is one sentence.

The sweep of every sentence defined feed, carry, IANA, multicast,
handler, streamer, reverse proxy and goroutine at first use, split the
list of parts, and named the 404 of an unknown page path.

Model: fable-5-1

internal/server/middleware_internal_test.go

@@ -261,7 +261,7 @@ func checkAnswerCarriesMeta(
 ) {
 	t.Helper()
 
-	// The values README "API v1" gives the two fields that never change.
+	// The values README "JSON API" gives the two fields that never change.
 	const (
 		wantTimeZone   = "UTC"
 		wantAPIVersion = 1