caddy: Updating docs for builder image changes

[hairyhenderson]

Changes relevant to docker-library/official-images#8735

Many thanks to @francislavoie for writing this 😉

Signed-off-by: Dave Henderson dhenderson@gmail.com

[francislavoie]

@yosifkit I hope you don't mind me asking like this on a merged PR.

Is there any way to dynamically replace this <version> with a placeholder? I dug through the scripts in this repo and I didn't find any relevant placeholders.

Ideally, I'd like a %%LATEST_VERSION%% placeholder that would basically be the version number that the latest tag shares.

I've already gotten a question from a user recently who is new to Docker asking "do I need to replace <version>?" so I think this should be improved.

[tianon]

Unfortunately, that's a somewhat complicated problem for us to solve generally, especially since in many cases using the "most specific" versioned tag isn't actually what we recommend users should use (PHP for example - most users should use X.Y not X.Y.Z so they continue to get patch updates and because that's the level at which compatibility is supposed to be kept between versions).