Docs: Expose transport port in dev example

Exposing the transport port helps testing of the transport client.

Relates:
#26289 (comment)

docs/reference/setup/install/docker.asciidoc

@@ -49,7 +49,7 @@ Elasticsearch can be quickly started for development or testing use with the fol
 
 ["source","sh",subs="attributes"]
 --------------------------------------------
-docker run -p 9200:9200 -e "discovery.type=single-node" {docker-image}
+docker run -p 9200:9200 -p 9300:9300 -e "discovery.type=single-node" {docker-image}
 --------------------------------------------
 
 endif::[]