Update README to provide more details on how this action works.

Author: khiga8

README.md

@@ -1,12 +1,19 @@
 # Accessibility-alt-text-bot
 
-An action to remind users to add alt text to their issue descriptions and comments.
+This action supports accessible content sharing on GitHub by leaving an automated reminder whenever an image is shared on a GitHub Issue or Pull request without meaningful alternative text (alt text).
+Alternative text helps convey the context of the image to those who use assistive technologies such as a screen reader and removes accessibility barriers.
+
+For guidance on setting alternative text, see [Alternative text for images on Primer](https://primer.style/design/guides/accessibility/alternative-text-for-images).
+
+Images on GitHub default to using the filename as alt text. This action flags when the alt text has not been updated from the default.
+
+**Note**: Ordinarily, setting `alt=""` will mark images as decorative. However, GitHub currently renders all images as a link. To avoid rendering links with no names, we recommend always setting alt text on images in GitHub.
 
 ## How to add this action to your repo
 
 Copy this workflow into any repo you want the accessibility-alt-text-bot to run in.
 
-```
+```yml
 name: Accessibility-alt-text-bot
 on: 
   issues:
@@ -26,22 +33,21 @@ jobs:
         uses: github/accessibility-alt-text-bot
 ```
 
-## Action stability
+### Action stability
 
 To ensure you stay on a stable version of this action consider locking the action to a specific version.
 
-```       
+```yml
        uses: github/[email protected]
-```    
+```
 
 Replace the ref value with any commit hash.
 
-## License 
+## License
 
 This project is licensed under the terms of the MIT open source license. Please refer to [MIT](./LICENSE.txt) for the full terms.
 
-
-## Maintainers 
+## Maintainers
 
 See [CODEOWNERS](.github/CODEOWNERS).