Explain consequence of toggling config variable

The 'concept_exercises' config variable could be misunderstood to mean that
a track has concept exercises, whereas in practice it is used to toggle
learning mode on or off for an entire track.

Toggling to 'false' allows track maintainers to build out concept exercises
without making them available on the site.

Author: kytrinyx

building/tracks/config-json.md

@@ -16,7 +16,7 @@ The following top-level properties contain general track metadata:
   - `indent_size`: the indentation size as an integer (e.g. `4`) (required)
   - `highlightjs_language`: the language identifier for Highlight.js (see the [full list of identifiers](https://github.com/highlightjs/highlight.js/blob/main/SUPPORTED_LANGUAGES.md)) (required)
 - `status`: an object describing which v3 features should be enabled: (required)
-  - `concept_exercises`: a `boolean` value indicating if [Concept Exercises](/docs/building/tracks/concept-exercises) have been built (required)
+  - `concept_exercises`: a `boolean` value indicating if [Concept Exercises](/docs/building/tracks/concept-exercises) have been built (required). When `true` the Exercism website interface changes to indicate that concept exercises are available for the track.
   - `test_runner`: a `boolean` value indicating if a [test runner](/docs/building/tooling/test-runners) has been implemented (required)
   - `representer`: a `boolean` value indicating if a [representer](/docs/building/tooling/representers) has been implemented (required)
   - `analyzer`: a `boolean` value indicating if an [analyzer](/docs/building/tooling/analyzers) has been implemented (required)