Update image test to add className and refresh screenshot

Add guidance in README to be selective when updating screenshots.

Author: jderochervlk

README.md

@@ -66,6 +66,7 @@ yarn vitest:update
 ```
 
 This runs the full suite headlessly with the `--update` flag, regenerating any screenshot baselines that have changed. Commit the updated `.png` files alongside your code changes.
+Please be selective in pushing up changes to screenshots and only update files that you have added or expected to change. Pushing up all changes can make it hard to review PRs with small image differences based on different devices or environments that wouldn't trigger failures in CI.
 
 ### Markdown Codeblock Tests
 

__tests__/MarkdownComponents_.test.res

@@ -203,7 +203,9 @@ test("renders Image with caption", async () => {
   let screen = await render(
     <div dataTestId="image-wrapper">
       <Markdown.Image
-        src="https://rescript-lang.org/lp/community-3.avif" caption="A sample image caption"
+        className="rounded-lg border border-gray-90/5 text-gray-60"
+        src="https://rescript-lang.org/lp/community-3.avif"
+        caption="A sample image caption"
       />
     </div>,
   )