Tweak and update subsection Labels of Issue Triaging

[fmease]

1. Mention more label categories that are of importance
   1. Mention PG-* labels (→ specific project groups).
   2. Mention L-* labels (→ specific lints).
   3. Mention -Z* labels (→ specific unstable -Z compiler flags).
2. Mark keywords bold / strong. With keyword I mean words (e.g., team) whose initial is used as the prefix of a label category (e.g., T-). https://rustc-dev-guide.rust-lang.org/contributing.html#issue-triage does this, too, which I found out after the fact.
3. Linkify label categories just like https://rustc-dev-guide.rust-lang.org/contributing.html#issue-triage.
4. Add three footnotes for "trivia" (can be used to form mnemonics :P).
5. Link to https://rustc-dev-guide.rust-lang.org/contributing.html#issue-triage.
6. Tiny style tweaks for consistency (periods, etc.).
7. Sort the list of important I-* labels by ... importance and add a two or three more labels.

NB: I haven't added a bullet point for the B-* labels (used on tracking issues & related to unstable language features) because they're not relevant for your everyday issue triaging in my opinion.

[jieyouxu]

Left some nits, but LGTM otherwise.

[apiraino]

I've tried looking at the rendered version and to be honest in the new proposed version there's so much formatting that I find it hard to visually parse the document.

Old version

New version

I can't pinpoint exactly all the small things that imo make the new version less readable, they are mixed with small improvements in the wording, which I find otherwise valuable.

I don't have time or energy (or UI skills) to make a detailed review so I won't oppose merging this as it is. I wish we had someone with some a11y background for an informed opinion.

Sorry @fmease I am a minimalist 😆

[jieyouxu]

I can't pinpoint exactly all the small things that imo make the new version less readable, they are mixed with small improvements in the wording, which I find otherwise valuable.

It's probably a mix of the label prefixs in different font, color and background + bolded keywords + monospace example labels that makes it a bit visually busy. Not sure how to make it less overwhelming either.

[fmease]

I can remove the links and the weight on the keywords again and only keep the wording tweaks. That'd be fine by me

[jieyouxu]

I can remove the links and the weight on the keywords again and only keep the wording tweaks. That'd be fine by me

I think it's nice fuctionally to have them lol

[Noratrieb]

mdbook is less noisy than GitHub, so the comparison isn't entirely fair. I think removing the emphasis makes sense, it's fairly obvious and not that important.

[Noratrieb]

thanks, cool. i'd be fine merging it as-is but if you wanna remove the emphasis and address some more feedback first that works too. just make sure to not get lost in improvements and forget the PR, rather merge early than late :)

[fmease]

I've addressed the review comments and removed the font weight from the keywords again but kept the links because they're quite useful imo even if they might worsen the UI slightly due to their blue color.