[a11y] Add documentation for the badge component (#1364)

* Add a11y documentation for the badge component
* Add entry for documentation change

UNRELEASED.md

@@ -30,6 +30,7 @@ Use [the changelog guidelines](https://git.io/polaris-changelog-guidelines) to f
 - Added accessibility guidance for `Heading` and `Subheading`. ([#1351](https://github.com/Shopify/polaris-react/pull/1351))
 - Added accessibility documentation for `List` and `Stack`. ([#1353](https://github.com/Shopify/polaris-react/pull/1353))
 - Added accessibility guidance for `DisplayText`. ([#1354](https://github.com/Shopify/polaris-react/pull/1354))
+- Added accessibility documentation for `Badge`. ([#1364](https://github.com/Shopify/polaris-react/pull/1364))
 
 ### Development workflow
 

src/components/Badge/README.md

@@ -265,3 +265,31 @@ Use to indicate when a given task has been completed. For example, when merchant
 ## Related components
 
 - To represent an interactive list of categories provided by merchants, [use tags](/components/forms/tag)
+
+---
+
+## Accessibility
+
+<!-- content-for: android -->
+
+See Material Design and development documentation about accessibility for Android:
+
+- [Accessible design on Android](https://material.io/design/usability/accessibility.html)
+- [Accessible development on Android](https://developer.android.com/guide/topics/ui/accessibility/)
+
+<!-- /content-for -->
+
+<!-- content-for: ios -->
+
+See Apple’s Human Interface Guidelines and API documentation about accessibility for iOS:
+
+- [Accessible design on iOS](https://developer.apple.com/design/human-interface-guidelines/ios/app-architecture/accessibility/)
+- [Accessible development on iOS](https://developer.apple.com/accessibility/ios/)
+
+<!-- /content-for -->
+
+<!-- content-for: web -->
+
+Badges that convey information with icons or color include text provided by the [visually hidden component](/components/titles-and-text/visually-hidden#navigation). This text is read out by assistive technologies like screen readers so that merchants with vision issues can access the meaning of the badge in context.
+
+<!-- /content-for -->