Improve Documentation

This change updates the documentation of Oracle JRE to describe how to use it
without a buildpack fork.

[resolves #383]

docs/jre-oracle_jre.md

@@ -27,6 +27,13 @@ For general information on configuring the buildpack, including how to specify c
 
 The JRE can be configured by modifying the [`config/oracle_jre.yml`][] file in the buildpack fork.  The JRE uses the [`Repository` utility support][repositories] and so it supports the [version syntax][]  defined there.
 
+To use Oracle JRE instead of OpenJDK without forking java-buildpack, set environment variable:
+
+`cf set-env <app_name> JBP_CONFIG_COMPONENTS '{ jres: [ "JavaBuildpack::Jre::OracleJRE" ] }'`
+`cf set-env <app_name> JBP_CONFIG_ORACLE_JRE '{ jre: { repository_root: "<INTERNAL_REPOSITORY_URI>" } }'`
+
+`cf restage <app_name>`
+
 | Name | Description
 | ---- | -----------
 | `memory_sizes` | Optional memory sizes, described below under "Memory Sizes".