Update docs for Caddy image with a fix to its reload feature

[BjoernLudwigPTB]

Last August unexpected behaviour of the graceful reload feature was discussed in this upstream issue and a fix proposed alongside the suggestion to add that fix to the docs. This has not yet happened but should be solved by this PR.

This is my first contribution here, so if there is anything I should address to finalize this PR, I ask you kindly to let me know.

[whalelines]

Looks reasonable to me, as long as there remains only a single file under the image's /etc/caddy directory.

[tianon]

Agreed, seems OK to me -- cc @hairyhenderson @francislavoie (caddy image maintainers)

[tianon]

(Looks like there's also a bit of trailing whitespace that our markdownfmt is balking at)

[francislavoie]

I don't agree with this wording/framing. This isn't quite true, it only breaks if you happen to be using vim/vi in which case the way it saves files isn't tracked properly by Docker. But if you use a different editor like nano then the issue doesn't happen.

So I would prefer if this warned about making note of which editor you use to edit the file, rather than saying that it "breaks reloading" in general.

[BjoernLudwigPTB]

Agree, I will come up with a better wording reflecting the actual scope of the circumstances in which there is something to warn about. I submitted this proposal from the perspective of someone having followed the documentation exactly and due to having used vim to edit the file, I ran into the described situation.

[BjoernLudwigPTB]

@francislavoie I have now suggested a wording that better reflects the situation that is causing the actual problem. This makes the paragraph a little lengthier, but also more precise. What do you think? Would you agree to these changes?

[francislavoie]

Suggested change

	Defining the data volume as [`external`](https://docs.docker.com/compose/compose-file/compose-file-v3/#external) makes sure `docker-compose down` does not delete the volume. You may need to create it manually using `docker volume create [project-name]_caddy_data`.
	Defining the data volume as [`external`](https://docs.docker.com/compose/compose-file/compose-file-v3/#external) makes sure `docker compose down` does not delete the volume. You may need to create it manually using `docker volume create [project-name]_caddy_data`.

[BjoernLudwigPTB]

In fact, now that we are talking about this section as well: May I suggest to delete this paragraph and the parameter external = true in the suggested compose.yaml as a docker compose down wouldn't actually delete the volume. One would need to provide an addional -v or --volumes in addition to loose its content. In many cases providing this flag additionally would cause damage to applications, which usually do not mention this in their sample configurations or examples as Docker users usually seem to be aware of the consequences. If you agree @francislavoie I would simply delete these two parts in another commit.

[BjoernLudwigPTB]

@francislavoie And please review my comment above and give your opinion on that.

• suggestion 1: remove this paragraph and the external = true parameter for the volume in the compose.yaml.
• option 2: Apply your suggested changes and leave everything else as is.