add tip for alt attribute for the add-images-to-your-website challenge (#16197)

challenges/01-responsive-web-design/basic-html-and-html5.json

@@ -619,6 +619,7 @@
         "<code>&#60img src=\"https://www.your-image-source.com/your-image.jpg\"&#62</code>",
         "Note that in most cases, <code>img</code> elements are self-closing.",
         "All <code>img</code> elements <strong>must</strong> have an <code>alt</code> attribute. The text inside an <code>alt</code> attribute is used for screen readers to improve accessibility and is displayed if the image fails to load.",
+        "Ideally the <code>alt</code> attribute should not contain special chars unless needed.",
         "Let's add an <code>alt</code> attribute to our <code>img</code> example above:",
         "<code>&#60img src=\"https://www.your-image-source.com/your-image.jpg\" alt=\"Author standing on a beach with two thumbs up.\"&#62</code>",
         "<hr>",
@@ -2242,4 +2243,4 @@
       "ru": {}
     }
   ]
-}
+}