Add documentation about giving hints to specific instruction steps

[fapdash]

Apparently it's possible to give hints to a specific step in the instructions.md: https://github.com/exercism/common-lisp/blob/149c61afdf0025f63e5a5dc1157e1b7882df65ff/exercises/concept/pizza-pi/.docs/hints.md?plain=1#L23-L27

Which shows up in the online editor like this:

I think that's really cool but I don't see this documented:

docs/building/tracks/practice-exercises.md

Lines 213 to 239 in 7926569

	### File: `.docs/hints.md`
	**Purpose:** Provide hints to a student to help them get themselves unstuck in an exercise.
	**Presence:** Optional
	- If the student gets stuck, we will allow them to click a button requesting a hint, which will show the relevant part of file.
	- Hints should be bullet-pointed underneath headings.
	- The hints should be enough to unblock almost any student.
	- The hints should not spell out the solution, but instead point to a resource describing the solution (e.g. linking to documentation for the function to use).
	- The hints may use code samples to explain concepts, but not to outline the solution. e.g. in a lists exercise they might show a snippet of how a certain list function works, but not in a way that is directly copy/pasteable into the solution.
	- The hints must appear as a Markdown list under a `## General` heading.
	- If there are no hints, the heading should be omitted.
	Viewing hints will not be a "recommended" path and we will (softly) discourage using it unless the student can't progress without it. As such, it's worth considering that the student reading it will be a little confused/overwhelmed and maybe frustrated.
	#### Example
	```markdown
	## General
	- There are many [built-in methods][integers] to simplify working with integers.
	[integers]: https://ruby-doc.org/core-2.7.0/Integer.html
	```
	---

Edit: I just realized that the example I gave is for a learning exercise, not a practice exercise, but since all exercises are moving to that format I assume that this will be possible for practice exercises following this format as well?

[fapdash]

Will there even be a difference between Concept Exercises and Practice Exercises or can the two documentation pages be merged?

Edit: Answered my own question, no they can't be merged, eg. concept exercises don't have a difficulty.

[fapdash]

Nevermind, practice exercises don't have instruction steps. Closing.