Mention defaults subdirectory in a more visible way

All examples do not show it, so only someone reading the doc from
end to end would know about it.
Merge pull request #8996 from mscherer/improve_doc_defaults

Mention defaults subdirectory in a more visible way
Fix splitting the tag from the image name

Fixes #8983
Ensure checkmode is honored for templates that haven't changed

Fixes #8998