yarn.md in licensed-3.4.0

- old
+ new
@@ -1,15 +1,16 @@
 # Yarn
 
 The yarn source will detect dependencies when `package.json` and `yarn.lock` are found at an app's `source_path`.
 
-It uses `yarn list` to enumerate dependencies and `yarn info` to get metadata on each package.
+It uses the `yarn` CLI commands to enumerate dependencies and gather metadata on each package.
 
-### Including development dependencies
+## Including development dependencies
 
-Yarn versions < 1.3.0 will always include non-production dependencies due to a bug in those yarn versions.
+**Note** Yarn versions < 1.3.0 will always include non-production dependencies due to a bug in those versions of yarn.
+**Note** Yarn versions > 2.0 will always include non-production dependencies due to lack of filtering of production vs non-production dependencies in the yarn CLI.
 
-Starting with yarn version >= 1.3.0, the yarn source excludes non-production dependencies by default.  To include development and test dependencies, set `production_only: false` in `.licensed.yml`.
+For yarn versions between 1.3.0 and 2.0, the yarn source excludes non-production dependencies by default.  To include development and test dependencies in these versions, set `production_only: false` in `.licensed.yml`.
 
 ```yml
 yarn:
   production_only: false
 ```