README: blocks misbehaving scrapers, not normal ones (closes #387)

The opening now lists what bans a client with the default settings: the
rate and byte limits, a probe for a secret path, a security scanner's
user agent, and the refusal limit. A scraper that does none of these is
left alone.

Model: opus-5-5

README.md

@@ -5,20 +5,17 @@
 requests of misbehaving scrapers, scanners and other abusers before they reach
 an app.
 
-It does not block scrapers as such. A scraper that stays within the limits below
-is left alone, whatever its user agent. With the default settings, a client is
-banned when it does any of these:
+With the default settings, a client is banned when it does any of these:
 
 - makes more than 120 requests in a minute, 1500 in an hour or 6000 in a day;
 - moves more than `50G` of request and response bodies in an hour, or `100G` in
   a day;
-- asks for a path no real visitor asks for, such as `/.env` or `/.git/config`;
+- asks for a secret or backup file, such as `/.env` or `/.git/config`;
+- sends a user agent that names a security scanner, such as `sqlmap` or `nikto`;
 - has more than 30 requests in a minute refused as probes or attacks.
 
-A scraper that waits 15 seconds between requests stays under every one of these
-limits. The user agent alone gets a client refused only when it names a security
-scanner, such as `sqlmap` or `nikto`. Settings you add, such as a refused
-country or a blocklist, can refuse any client.
+A scraper that does none of these is left alone. A scraper that waits 15 seconds
+between requests stays under the rate limits.
 
 ## What it does