Document that rules are not for creating by the thousands

This addresses #5433, which featured a user attempting to create 30k rules.

diff --git a/pdns/README-dnsdist.md b/pdns/README-dnsdist.md
index 1a8c0a6adff90cf60964f48f87ea277456b42405..827a7e9007147511f2680f717f493e6f27b8c562 100644 (file)
--- a/pdns/README-dnsdist.md
+++ b/pdns/README-dnsdist.md
@@ -471,6 +471,7 @@ single operation with `setRules()`:
 > setRules( { newRuleAction(TCPRule(), AllowAction()), newRuleAction(AllRule(), DropAction()) } )
 ```
 
+NOTE: Adding large numbers of rules (200+) is slow, and will also impact performance significantly. Instead of creating numerous rules, consider using smaller numbers of individual rules that match large numbers of domains or IP addresses, for example using a `SuffixMatchNodeRule` or a `NetmaskGroupRule`. These rules are optimized for hosting thousands or millions of domain names or IP addresses. 
 
 More power
 ----------