Update the section on jenkins changes for a new branch.
Update the section on jenkins changes for a new branch.

This reflects the actual state of things at the moment.
There is quite a bit of assumed knowledge here in a rapidly changing
(test) environment.

referencing #22672.

bgrant0607/community,kubernetes/community,kubernetes/community,bgrant0607/community,kubernetes/community,pwittrock/community,pwittrock/community