update image documentation based on recent discussion

Author: khiga8

docs/rules/accessibility/no-redundant-image-alt.md

@@ -4,6 +4,9 @@
 
 `<img>` alt prop should not contain `image` or `picture` as screen readers already announce the element as an image.
 
+This rule does not discourage conveying the _medium_ of the image which may be considered important to help a user better understand the content.
+For example, this rule will not flag terms including `screenshot`, `painting`, or `photograph`.
+
 Learn more at [W3C WAI Images Tutorial](https://www.w3.org/WAI/tutorials/images/).
 
 ### 👎 Examples of **incorrect** code for this rule:
@@ -12,15 +15,24 @@ Learn more at [W3C WAI Images Tutorial](https://www.w3.org/WAI/tutorials/images/
 <img alt="picture of Mona Lisa" src="monalisa.png">
 ```
 
+```erb
+<!-- also bad -->
+<img alt="image of a fluffy dog" src="monalisa.png">
+```
+
 ### 👍 Examples of **correct** code for this rule:
 
 ```erb
 <!-- good -->
 <img alt="Mona Lisa" src="monalisa.png">
 ```
 
-
 ```erb
 <!-- also good -->
 <img alt="The original painting of Mona Lisa hangs on the wall of Louvre museum" src="monalisa.png">
 ```
+
+```erb
+<!-- also good -->
+<img alt="Screenshot of the user profile Settings page, with the 'Notifications' item highlighted" src="settings_page.png">
+```