update README with information about versioning featured links

Author: sarahs

data/learning-tracks/README.md

@@ -19,9 +19,11 @@ Learning track data for a product is defined in two places:
 
 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.
+    For example, in `data/learning-tracks/actions.yml`, each of the items from the content file's `learningTracks` array is represented with additional data such as `title`, `description`, and an array 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. A test will fail if this property is missing.
+    One learning track in this YAML **per version** 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. A test will fail if this property is missing.
+
+    The `featured_track` property can be a simple boolean (i.e., `featured_track: true`) or it can be a string that includes versioning statements (e.g., `featured_track: '{% if currentVersion == "free-pro-team@latest" %}true{% else %}false{% endif %}'`). If you use versioning, you'll have multiple `featured_track`s per YML file, but make sure that only one will render in each currently supported version. A test will fail if there are more or less than one featured link for each version.
 
 Versioning for learning tracks is processed 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`.