Add docker image building instructions

Author: mkumatag

guestbook/README.md

@@ -40,6 +40,30 @@ Download the following configuration files:
 
 {% capture lessoncontent %}
 
+## Building the Docker images
+
+```console
+$ docker build -t gcr.io/google-samples/gb-frontend:v5 php-redis
+
+$ docker build -t gcr.io/google-samples/gb-redisslave:v2 redis-slave
+```
+
+Building Multi-architecture docker images
+
+```console
+$ make -C php-redis
+
+$ make -C redis-slave
+```
+
+Push:
+
+```console
+$ make -C php-redis all-push
+
+$ make -C redis-slave all-push
+```
+
 ## Start up the Redis Master
 
 The guestbook application uses Redis to store its data. It writes its data to a Redis master instance and reads data from multiple Redis slave instances.