update concept about.md explanation

[junedev]

exercism/javascript#1021 triggered a discussion about the intended content of the about.md file.

This PR is indented to improve the documentation for a concepts' about.md file. The old version contained some artifacts from the old "after.md of an exercise" approach what resulted in misunderstandings.

The new explanation is based mainly on the input @iHiD gave in Slack.

I replaced the example to use something that included a common pitfall to better illustrate the difference to the introduction.md file.

Additional info I would like to include if someone can provide them:

• How to properly link to another concept? I have seen links like https://exercism.lol/tracks/ruby/concepts/conditionals but those would need to be replaced later.
• How exactly would a student reach the about.md page?

[SleeplessByte]

Looking great. Here are at least two answer:

How to properly link to another concept? I have seen links like exercism.lol/tracks/ruby/concepts/conditionals but those would need to be replaced later.

These three things will work:

• https://exercism.lol/tracks/ruby/concepts/conditionals. It works right now, so this is what I used in the JavaScript docs. The site will correctly replace the domain with the "active domain" right before render.
• https://exercism.io/tracks/ruby/concepts/conditionals. It doesn't work right now (until we launch v3), but feels a bit more correct once we do. Same result as above.
• /tracks/ruby/concepts/conditionals. Starting with a / with be replaced with the "active domain". The link never works except when rendering on the site, but feels canonically most correct.

How exactly would a student reach the about.md page?

1. Via the concept tree (e.g. https://exercism.lol/tracks/javascript/concepts), then clicking on a concept.
2. Via a different concept page.
3. Via any other document that supports markdown, because there can be direct links and widgets to these concept pages.
4. Clicking the concept on https://exercism.lol/tracks/javascript/exercises/basics (after completion, but also before, I think).

[iHiD]

How to properly link to another concept? I have seen links like https://exercism.lol/tracks/ruby/concepts/conditionals but those would need to be replaced later.

There's info on this in the linking doc: https://github.com/exercism/docs/blob/main/anatomy/tracks/internal-linking.md

How exactly would a student reach the about.md page?

The about.md becomes the content on a Concept page (e.g. https://exercism.lol/tracks/javascript/concepts/basics) once that Concept has been learnt. Before the concept has been learnt, the introduction.md shows instead.

[iHiD]

This looks really good. Thank you. I've made a few small suggestions and capitalized Concept and Exercise throughout as they're considered proper nouns within Exercism.

I'd also like to get @ErikSchierboom to sign it off before it gets merged.

[junedev]

@iHiD Thanks for the fixes and additions! I accepted the suggestions and also added the link to the "internal linking" document you provided.

[ErikSchierboom]

Excellent work! I've left some small nits.

[junedev]

@ErikSchierboom Thanks for the feedback. 😊 Changes are included now.

[ErikSchierboom]

LGTM Thanks! 🎉