Add details of interaction

Describes more clearly the interaction between the Docker Client, the Docker Dameon and Docker Hub.

beginner/chapters/alpine.md

@@ -30,7 +30,13 @@ drwxr-xr-x    5 root     root          4096 Mar  2 16:20 lib
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-What happened? Behind the scenes, a lot of stuff happened. When you call `run`, the Docker client finds the image (alpine in this case), creates the container and then runs a command in that container. When you run `docker run alpine`, you provided a command (`ls -l`), so Docker started the command specified and you saw the listing.
+What happened? Behind the scenes, a lot of stuff happened. When you call `run`, 
+1. The Docker client contacts the Docker daemon
+2. The Docker daemon dowloads the image (alpine in this case) from Docker Hub
+3. The Docker daemon creates the container and then runs a command in that container. 
+4. The Docker daemon streams the output of the command to the Docker client
+
+When you run `docker run alpine`, you provided a command (`ls -l`), so Docker started the command specified and you saw the listing.
 
 Let's try something more exciting.