refer to the registry instead of the hub

Signed-off-by: Jeff Anderson <jeff@docker.com>
Update dockerimages.md

remove 'public registry'

Signed-off-by: Jeff Anderson <jeff@docker.com>
Webhooks documentation: second pass addressing @fredlf's comments

Signed-off-by: Joffrey F <joffrey@docker.com>
Merge pull request #9273 from programmerq/dockerimages_hub

refer to the registry instead of the hub
Merge pull request #9460 from shin-/docs_webhooks2

Webhooks documentation: additional improvements