Document how to create a custom CLI build
Document how to create a custom CLI build

Document how to create a custom pex that you can use to put deployment-specific customizations.

Reviewed at https://reviews.apache.org/r/52884/

crashlytics/aurora,medallia/aurora,rdelval/aurora,crashlytics/aurora,medallia/aurora,apache/aurora,rdelval/aurora,apache/aurora,rdelval/aurora,rdelval/aurora,apache/aurora,thinker0/aurora,medallia/aurora,crashlytics/aurora,medallia/aurora,crashlytics/aurora,crashlytics/aurora,apache/aurora,medallia/aurora,crashlytics/aurora,apache/aurora,rdelval/aurora,apache/aurora,thinker0/aurora,thinker0/aurora,thinker0/aurora,rdelval/aurora,thinker0/aurora,medallia/aurora,thinker0/aurora