Docs: Fix pre-formatting for ratelimit plugin

doc/admin-guide/plugins/rate_limit.en.rst

@@ -84,26 +84,34 @@ This example shows a simple rate limiting of `128` concurrently active client
 transactions, with a maximum queue size of `256`. The default of HTTP status
 code `429` is used when queue is full.
 
+::
+
     map http://cdn.example.com/ http://some-server.example.com \
       @plugin=rate_limit.so @pparam=--limit=128 @pparam=--queue=256
 
 
 This example would put a hard transaction (in) limit to 256, with no backoff
 queue, and add a header with the transaction delay if it was queued:
 
+::
+
     map http://cdn.example.com/ http://some-server.example.com \
       @plugin=rate_limit.so @pparam=--limit=256 @pparam=--queue=0 \
       @pparam=--header=@RateLimit-Delay
 
 This final example will limit the active transaction, queue size, and also
 add a `Retry-After` header once the queue is full and we return a `429` error:
 
+::
+
     map http://cdn.example.com/ http://some-server.example.com \
       @plugin=rate_limit.so @pparam=--limit=256 @pparam=--queue=1024 \
       @pparam=--retry=3600 @pparam=--header=@RateLimit-Delay
 
 In this case, the response would look like this when the queue is full:
 
+::
+
     HTTP/1.1 429 Too Many Requests
     Date: Fri, 26 Mar 2021 22:42:38 GMT
     Connection: keep-alive