Updated custom builder description

creating_images/custom.adoc

@@ -12,9 +12,11 @@ toc::[]
 == Overview
 link:../architecture/core_objects/builds.html#custom-build[Custom build] is designed
 to fill the gap that was created when everybody jumped into creating docker images.
-Still there is a requirement to produce packages with all the software being installed
-and most importantly one needs to be able to build base docker images. This is
-where Custom build is the perfect match to fill in that gap.
+Still there is a requirement to produce individual artifacts (packages, jars, wars,
+installable zips, base images etc.) This is where Custom build is the perfect match
+to fill in that gap. Additionally Custom build allows implementing any extended build
+process for example, CI/CD flow that runs unit or integration tests. The limit here
+is just the imagination of the custom builder image author.
 
 To fully utilize the power of Custom build one needs to be understand how to
 create a builder image that will be capable of building desired objects.
@@ -38,3 +40,15 @@ the information needed to proceed with the build:
 |`*DOCKER_SOCKET*`
 |This variable specifies the path to docker socket, if exposing docker socket was enabled on BuildConfig.
 |===
+
+== Custom builder workflow
+Although custom builder image author has a great flexibility in defining the build
+process on its own, still he should follow a few required steps necessary to seamlessly
+run a build inside of OpenShift. The required steps for a custom builder image are following:
+
+. Read the link:../rest_api/openshift_v1.html#v1-build[Build] definition, which
+contains all the necessary information about input parameters for the build.
+. Run the build process.
+. If your build produces image, push it to the link:../rest_api/openshift_v1.html#v1-build[Build]'s
+output location if the output location is defined. Other output locations can be passed with environment
+variable for now.