HLD: Accessible labels and localization in Nimble (#1272)

# Pull Request

## 🤨 Rationale

#1090

## 👩‍💻 Implementation

N/A (HLD and doc updates)

## 🧪 Testing

N/A

## ✅ Checklist

- [x] I have updated the project documentation to reflect my changes or
determined no changes are needed.

change/@ni-nimble-components-2dda6a9d-d30f-45f2-b086-f5564c763990.json

@@ -0,0 +1,7 @@
+{
+  "type": "none",
+  "comment": "Update docs (accessible labels for button/banner/icons)",
+  "packageName": "@ni/nimble-components",
+  "email": "[email protected]",
+  "dependentChangeType": "none"
+}

packages/nimble-components/docs/accessibility.md

@@ -26,5 +26,18 @@ When setting [ARIA attributes](https://developer.mozilla.org/en-US/docs/Web/Acce
 
 # Component-specific accessiblity notes
 
-## nimble-button
-When using the `nimble-button` with only an icon, `contentHidden` should be set to `true` and text content should be provided within the button even though it will not be visible on the screen. The button will use the text content to configure the appropriate ARIA attributes internally to ensure the button is adequately accessible with a screen reader.
+## Buttons
+`nimble-button`, `nimble-anchor-button`, `nimble-menu-button`, `nimble-toggle-button`
+
+When using the Nimble buttons with only an icon, `contentHidden` should be set to `true` and text content should be provided within the button even though it will not be visible on the screen. The button will use the text content to configure the appropriate ARIA attributes internally to ensure the button is adequately accessible with a screen reader.
+
+## nimble-banner
+When using `nimble-banner`, the title content should always be provided for accessibility. To hide the title visually, `titleHidden` can be set to `true`.
+
+## nimble-dialog
+When using `nimble-dialog`, the title content should always be provided for accessibility. To hide the title visually, `headerHidden` can be set to `true`.
+
+## Icons
+When using an icon standalone, the `title` attribute should usually be set, to provide accessible text (which will also show as a tooltip).
+
+When using an icon as the content of a Nimble button, place the icon in the `start` slot, and follow the button guidance above.