sha*sum: add more information link

[marchersimon]

For #5510

wait.......

[bl-ue]

@marchersimon please see @vladimyr's PR #5658 where he shorted the coreutils links.

[marchersimon]

I tried that, but that doesn't work here, since the url is sligthly different from the other pages.

[bl-ue]

Yeah, I just discovered that myself. Well, never mind 😛

[bl-ue]

Though the linked page is tiny (this is all of the text content, Ctrl+A - Ctrl+C):

Previous: sha1sum invocation, Up: Summarizing files [Contents][Index]

6.7 sha2 utilities: Print or check SHA-2 digests

The commands sha224sum, sha256sum, sha384sum and sha512sum compute checksums of various lengths (respectively 224, 256, 384 and 512 bits), collectively known as the SHA-2 hashes. The usage and options of these commands are precisely the same as for md5sum and sha1sum. See md5sum invocation.

...there's that link at the end which is pretty obvious IMO. But if the others think, maybe we should change the links to all point to that md5sum link. 🤔

[marchersimon]

The problem I have with directly linking to the md5sum page, is that nowhere in the page is mentioned that those arguments also work for the sha*sum pages, which will probably confuse many and make it seem the link is wrong.

[bl-ue]

@navarroaxel, @glenacota, @YUTYO Someone, can we get this merged? I'd like to incorporate it into #5664 before that gets merged.