proposal: "archived" resources

[eshellman]

In #6281 @LuigiImVector implements a suggestion to mark items that have been changed to a wayback machine link to add an access note (:card_file_box: archived) (I think I saw this on another PR, too) used by @davorpa in #6276

I indtend to merge that PR in a few days, as I think this is a useful addition, but I wonder if this should be our standard practice, i.e. added to our documentation (#6282). Or do users/contribuotrs feel this clutters the UI or is difficult to implement, or could be improved?

Comments/suggestions welcomed!

[davorpa]

(I think I saw this on another PR, too)

You are right. It's something liked in #5464 (comment), PR where I used it in as first time.

Here the repo search about it: https://github.com/EbookFoundation/free-programming-books/search?q=archive.org

I agree with it is a nice visual touch, and also maybe related with some historical resources we list and not recoverable using other ways.

As I mention in #5470 about recovering process

First look up for an alternative link:

1. Try to change protocol http-https.
2. On the same site. Maybe was moved due to a website redesign.
3. In the author/editorial/publisher site
4. In The Wayback Machine or Unglue.it
5. In third-party websites, specially public libraries, universities or colleges.

If in none of ⬆️ was found, then delete it

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Syntaxes:

01:   _(:card_file_box: archived)_
02:   *(:card_file_box: archived)*

both format notes as italic