docs: clarify and improve docker dev docs

docs: clarify and improve docker dev docs

The docker dev docs:

 - had the links for docker and docker-compose swapped.

 - had a old docker install link.

 - lacked an up-front explanation of the requirement that a regular user
   be able to manage the docker daemon (and a fairly unhelpful reference
   link in the most appropriate note block.)

Fix it all.

Reported-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>