doc: fix man pages link to signal

[DiegoRBaquero]

This add the space needed to match the man pages linking regex.

Refs: #17724

Checklist

• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

doc

[Trott]

I'd greatly prefer to fix the regular expression rather than force white space changes that really ought to have no effect.

[DiegoRBaquero]

@Trott I agree with you, the regex must be fixed.

Anyhow, this PR improves readability of that paragraph.

[maclover7]

Closing since #17724 was landed and fixed original issue. Please reopen if still needed.

[DiegoRBaquero]

@maclover7 I would still merge this. As I said before, it improves readability of that paragraph.

[Trott]

I'm unconvinced that this is an improvement. I don't think this substantially improves readability, and it introduces an idiosyncratic line-wrapping that (AFAIK) we don't do anywhere else. (Docs are wrapped at 80 chars, not one-line-per-sentence.)

(That said, I'm stoked that the regexp was improved in the related PR!)

[DiegoRBaquero]

Alright :)