Record measured rate-limit behaviour per engine

Concrete numbers from development rather than a vague warning: Google
tolerates a lot then blocks for ~90 minutes, Brave challenges after one or
two queries and clears in ~15-20, and DuckDuckGo and Bing never challenged
at all. That last fact is the useful one — it says which engine to reach
for when several searches are needed in a row.

1 files changed, 8 insertions, 4 deletions

diff --git a/README.md b/README.md
index 684bd96..6dac8a7 100644
--- a/README.md
+++ b/README.md
@@ -121,10 +121,14 @@ The browser is shared and belongs to a person. Worth being aware of:
   in the search engine's account history if that profile is signed in.
 - Tabs open and close on someone's screen. `background: true` keeps them from
   stealing focus, but they are visible.
-- Searching hard trips rate limiters for the whole host — a handful of queries in
-  a few seconds is enough to earn a challenge that affects the human using that
-  browser too. Measured on Google: roughly 30 queries in a few minutes cost about
-  90 minutes of blocking. Brave challenges considerably sooner than that.
+- Searching hard trips rate limiters for the whole host, and the challenge
+  affects the human using that browser too. Measured during development:
+  **Google** tolerated a lot, then roughly 30 queries in a few minutes cost about
+  90 minutes of blocking. **Brave** is far stricter — it challenges after as few
+  as one or two queries and clears again in roughly 15–20 minutes. **DuckDuckGo**
+  and **Bing** never challenged once across the whole of development, which is
+  why DuckDuckGo is the one to reach for when you need to run several searches
+  in a row.
 - **A decaying block does not look like a block.** Once the challenge page stops
   being served, engines return an *empty results page* for a while instead —
   indistinguishable from a query with no hits. It surfaces as `NoResultsError`,