Improve cf push examples

Previously, the examples in this repository for pushing applications
read as `cf push -b https://github.com/cloudfoundry/java-
buildpack.git`.  While this would work in cases where there was a
manifest for the application, it lead to confusion among users.

This change makes the examples more verbose, but much more clear and,
we hope, reduce the amount of confusion.

see: https://groups.google.com/a/cloudfoundry.org/d/topic/vcap-dev/ROJfb0SJ5PA/discussion

[#68430712]
Merge 68430712-cf-push to master

[Completes #68430712]