Follow-up from "✨ Add check writing guidance"

The following discussions from !55 (merged) should be addressed:

@manuelgrabowski started a discussion:
```
At a high level, the check contribution workflow looks like this:
```
Nitpick: Slightly more clarity without should/would etc.
@manuelgrabowski started a discussion:
```
You are encouraged to [install Lefthook](#installing-lefthook). Doing so ensures that the commands defined in `lefthook.yml` are executed when you commit or push changes. This will help you to find and fix problems with your contribution before the merge request pipeline catches them. 
```
I think we should only link to the local instructions, because it really is that simple. Two commands, that's it. They will work if you followed the other setup instructions. I just did it on my new laptop two days ago. If I instead look at https://lefthook.dev/installation/index.html I already have no desire anymore to find out what incantations I need to perform to get this set up. I also edited it to avoid using the word "check" in that sentence – I agree it is perfect to describe what is defined in lefthook.yml, but I think avoiding to reuse the term we use ourselves is worth the tradeoff of the worse term "commands".
@manuelgrabowski started a discussion:
This doesn't seem distinct enough to me from the sentence above. (I'd instead start arguing if "historically" is the right term here, does that not mean they already stopped causing widespread problems? If so, why do we need checks? Instead of deliberating, I'd suggest we drop the sentence.)
@manuelgrabowski started a discussion:
```
- GitLab Runner checks
```
Too vague, imo. To me, the complexity is due to fleet/node management for Runner hosts usually being separate from GitLab nodes, but I'm not sure we have to specify that.

  - Use commonly available executables like `grep`. Do not use executables like `rg` (`ripgrep`) that may not be installed on the customer's system. Consider using `grep -E` so that the pattern you pass is interpreted as an extended regular expression.
I'd still prefer striking that. Given that spot "eats" that output, I think this just complicates checks ever so slightly more for no benefit.

@manuelgrabowski started a discussion:

The `command` must be a single command, not just a one-liner. For example: `echo hello; echo world` is two commands on one line; however, combining them in a subshell via `$(echo hello; echo world)` is one command.
I worry this may be a bit too brief to not be confusing for folks who don't know/understand this already.

Edited May 02, 2025 by Brie Carranza