docs(targets): document shadowRoot capabilities

Author: keithamus

docs/_guide/targets.md

@@ -121,6 +121,12 @@ To clarify the difference between `@target` and `@targets` here is a handy table
 | `@target`  | `querySelector`          | `data-target="*"`  | `Element`        | 
 | `@targets` | `querySelectorAll`       | `data-targets="*"` | `Array<Element>` | 
 
+### Targets and "ShadowRoots"
+
+Custom elements can create encapsulated DOM trees known as "Shadow" DOM. Catalyst targets support Shadow DOM by first traversing the `shadowRoot`, if present.
+
+Important to note here is that nodes from the `shadowRoot` get returned _first_. So `@targets` will return an array of nodes, where shadowRoot nodes are at the start of the Array, and `@target` will return a ShadowRoot target if it exists, otherwise it will fall back to traversing the elements direct children.
+
 ### What about without Decorators?
 
 If you're using decorators, then the `@target` and `@targets` decorators will turn the decorated properties into getters.