remove unnecessary docker build, add TIP

Author: Xronophobe

chapter_09_docker.asciidoc

@@ -1091,9 +1091,11 @@ But we're just mapping 8888 to 8888, and that will look like this:
 
 [subs="specialcharacters,quotes"]
 ----
-$ *docker build -t superlists . && docker run -p 8888:8888 -it superlists*
+$ *docker run -p 8888:8888 -it superlists*
 ----
 
+TIP:  We don't need to run `docker build` this time since we have not changed our Dockerfile.
+
 Now that will _change_ the error we see, but only quite subtly (see <<firefox-connection-reset>>).
 Things clearly aren't working yet.