Seventh review: false statements fixed, README shortened to link the spec

- Engine error handling dropped as not built; unknown country and AS
  number each on its own; observe mode makes no ban of its own.
- README no longer restates the request steps, the refusal answers or
  the design; its step list uses the spec's numbers.
- Repeats, misreadable sentences, late verbs and long sentences reworded
  as the review asks.

Model: fable-5-1

docs/settings.md

@@ -196,8 +196,7 @@ that take `off`, the `_FILE` form, and what each group does and why.
 - `SWWAF_WAF_BODY_LIMIT` (default `off`): `off`, or how much of a request body
   the Core Rule Set reads, a size of at most `1G`.
 - `SWWAF_ERROR_BURST_THRESHOLD` (default `30`): the most refusals of one client
-  in a minute for a rule match, a trap path, a Core Rule Set match or a failed
-  token check. A count or `off`.
+  in a minute (see "Attack detection" in `SPEC.md`). A count or `off`.
 
 ## Ban lengths, response and scope