Various tweaks to example documentation & helpers.

Fixed the "starting" URL referenced in README - /whoami does not
exist any more, so following the instructions gave a "Not Found"
error.

Re-ordered the README sections to put things needed most often or
by more users up front; moved things most people will not need to
know towards the end.  (Very little content is new/changed; most
is just rearranged.)

Updated create_key.sh to be more test-friendly, and document how
to deploy newly generated keys; added a pointer to it in README.