Update documentation

cd/README.md

@@ -61,9 +61,17 @@ The [release job](Jenkinsfile_release_job) takes five parameters:
  * **MXNET_VARIANTS**: A comma separated list of variants to build. Defaults to *all* variants.
  * **RELEASE\_JOB\_NAME**: A name for this release job (Optional). Defaults to "Generic release job". It is used for debug output purposes.
  * **RELEASE\_JOB\_TYPE**: Defines the release pipeline you want to execute.
+ * **COMMIT_ID**: The commit id to build
 
 The release job executes, in parallel, the release pipeline for each of the variants (**MXNET_VARIANTS**) for the job type (**RELEASE\_JOB\_TYPE**). The job type the path to a directory (relative to the `cd` directory) that includes a `Jenkins_pipeline.groovy` file ([e.g.](mxnet_lib/static/Jenkins_pipeline.groovy)).
 
+The **COMMIT_ID** is a little tricky and we must be very careful with it. It is necessary to ensure that the same commit is built through out the pipeline, but at the same time, it has the potential to change the current state of the release job configuration. This means it is only provides forward compatibility with the current state of the job. That is, only commits that come after the current state of the pipeline, should be guaranteed to succeed.
+
+It should be noted that the 'Pipeline' section of the configuration should use the *$COMMIT_ID* parameter as the specifier and 'lightweight checkout' unchecked. For example:
+
+![job setup example](img/job_setup.png)
+<img width="1287" alt="Screen Shot 2019-09-18 at 8 05 47 PM" src="https://user-images.githubusercontent.com/785683/65173796-e291fa80-da4f-11e9-8b1f-aeb9d0781f26.png"> 
+
 ### Release Pipelines: Jenkins_pipeline.groovy
 
 This file defines the release pipeline for a particular release channel. It defines a function `get_pipeline(mxnet_variant)`, which returns a closure with the pipeline to be executed. For instance: