Add a11y note on external link

src/_components/link/index.md

@@ -129,6 +129,7 @@ Refer to the [Content Style Guide on Links]({{ site.baseurl }}/content-style-gui
 - **Keyboard navigation.** The user must be able to navigate to links using the Tab key and activate links using the Enter key.
 - **Purpose and target.** Link text that doesn't indicate a clear purpose or destination makes it harder for everyone--especially screen reader users--to understand where they're getting routed off to.
 - **External links must indicate that they are external.** Follow the methods detailed in [linking to external sites]({{ site.baseurl }}/content-style-guide/links#linking-to-external-sites).
+  - By default, the link component's external link variation will append the text, "(opens in a new tab)", instead of using an icon. This follows [Techniques for WCAG 2.0](https://www.w3.org/TR/WCAG20-TECHS/G201.html) advice on providing users with both a spoken and visual warning that this link opens in a new tab.
 
 {% include content/links-vs-buttons.md %}