Update docs on renaming existing package

[ericphanson]

To mention the old package's URL should be updated. cc @oxinabox who wrote the original version

[DilumAluthge]

@ericphanson @oxinabox Is this good to merge?

[ericphanson]

I think so. Do you think the link is OK? That was the only PR I could find which actually did the thing I suggest to do here, but the main PR body has a lot of discussion which I thought could confuse people.

[DilumAluthge]

Hmmm. Maybe pick a simpler PR?

[DilumAluthge]

Or just omit the PR link. I agree that the discussion in that PR will probably be overwhelming and not terribly useful.

[DilumAluthge]

Suggested change

	registry for the old package name to point to the new URL ([example](https://github.com/JuliaRegistries/General/pull/11578/files)).
	registry for the old package name to point to the new URL.

[ericphanson]

These are the repos whose URL in the registry redirects to another URL (ignoring .git ending differences):

original_repo	final_repo
https://github.com/sunoru/RandomNumbers.jl.git	https://github.com/JuliaRandom/RandomNumbers.jl
https://github.com/christopher-dG/GitForge.jl.git	https://github.com/JuliaWeb/GitForge.jl
https://github.com/zekeriyasari/Jusdl.jl.git (#40190)	https://github.com/zekeriyasari/Causal.jl
https://github.com/kul-forbes/ProximalOperators.jl.git (#40192)	https://github.com/kul-optec/ProximalOperators.jl
https://github.com/logankilpatrick/Slack.jl.git (#40193)	https://github.com/JuliaLangSlack/Slack.jl

(edit: crossed-out ones which have already been updated).

as of a couple weeks ago when I ran

get_url_after_redirect(url) = readchomp(`curl -ILs -o /dev/null -w %\{url_effective\} $url`)

# GitHub does not like this and will block you temporarily:
repo_redirects_df = let
	repo_redirects_df = DataFrame(:original_repo => unique(df.repo))
	repo_redirects_df.final_repo = asyncmap(get_url_after_redirect, repo_redirects_df.original_repo)
	repo_redirects_df
end

Arrow.write("repo_redirects.arrow", repo_redirects_df)

and got suspended from GitHub for a day for not rate-limiting when preparing my JuliaCon talk with Mosè about how many packages have docs/tests/ci/license/# lines of code/etc in General.

Of those, only one is a rename (Jusdl to Causal). So I will just make the PR to do the rename, and then link to that PR here 😄.