update internal docs

Author: sarahs

content/README.md

@@ -207,7 +207,7 @@ defaultPlatform: linux
 - type: `String`. This should reference learning tracks' names defined in [`data/learning-tracks/*.yml`](../data/learning-tracks/README.md).
 - Optional
 
-**Note: the first learning track is by-default the featured track.*
+**Note: the featured track is set by a specific property in the learning tracks YAML. See that [README](../data/learning-tracks/README.md) for details.*
 
 ### `includeGuides`
 - Purpose: Render a list of articles, filterable by `type` and `topics`. Only applicable when used with `layout: product-sublanding`.

data/learning-tracks/README.md

@@ -1,3 +1,28 @@
 # Learning Tracks (aka Learning Paths)
 
-Learning tracks are a collection of articles that help you master a particular subject. Learning tracks are defined on a per-product basis.
+Learning tracks are a collection of articles that help you master a particular subject. Learning tracks are defined on a per-product basis. For example, see https://docs.github.com/en/actions/guides.
+
+Learning track data for a product is defined in two places:
+
+1. A simple array of learning track names is defined in the product sublanding index page frontmatter.
+
+    For example, in `content/actions/guides/index.md`:
+    ```
+    learningTracks:
+      - getting_started
+      - continuous_integration
+      - continuous_deployment
+      - deploy_to_the_cloud
+      - hosting_your_own_runners
+      - create_actions
+    ```
+
+2. Additional data for each track is defined in a YAML file named for the **product** in the `data` directory.
+
+    For example, in `data/learning-tracks/actions.yml`, each of the items from the list in #1 is represented with additional data such as `title`, `description`, and a list of `guides` links.
+
+    One, and only one, learning track in this YAML must be designated as a "featured" learning track via `featured_track: true`, which will set it to appear at the top of the product sublanding page. Schema validation will fail if this property is missing.
+
+Versioning for learning tracks happens at page render time. The code lives in [`lib/learning-tracks.js`](lib/learning-tracks.js), which is called by `page.render()`. The processed learning tracks are then rendered by `layouts/product-sublanding.html`.
+
+The schema for validating the learning track YAML lives in [`tests/helpers/schemas/learning-tracks-schema.js`](tests/helpers/schemas/learning-tracks-schema.js) and is exercised by [`tests/content/lint-files.js`](tests/content/lint-files.js).