Merge pull request openshift#3411 from bfallonf/from_1403385

Bug 1403385 added from section to custom builds

Author: Brice Fallon-Freeman

dev_guide/builds.adoc

@@ -523,6 +523,25 @@ The following options are specific to the
 xref:../architecture/core_concepts/builds_and_image_streams.adoc#custom-build[Custom
 build strategy].
 
+[[custom-strategy-from]]
+
+=== FROM Image
+
+Use the `customStrategy.from` section to indicate the image to use for the
+custom build:
+
+====
+[source,yaml]
+----
+strategy:
+  type: "Custom"
+  customStrategy:
+    from:
+      kind: "DockerImage"
+      name: "openshift/sti-image-builder"
+----
+====
+
 [[expose-docker-socket]]
 
 === Exposing the Docker Socket