add alt text to all images

Author: lintsang

Wireframe/index.html

@@ -26,7 +26,7 @@ <h2>1. What is the purpose of a README file?</h2>
       </article>
       <article>
         <div class="image-wrapper">
-          <img src="https://cdn.iconscout.com/icon/premium/png-512-thumb/wireframe-icon-svg-download-png-10585798.png" alt="" />
+          <img src="https://cdn.iconscout.com/icon/premium/png-512-thumb/wireframe-icon-svg-download-png-10585798.png" alt="illustator of a wireframe icon" />
         </div>
         <h2>2. What is the purpose of a wireframe?</h2>
         <p>
@@ -36,7 +36,7 @@ <h2>2. What is the purpose of a wireframe?</h2>
       </article>
       <article>
         <div class="image-wrapper">
-          <img src="https://cdn.iconscout.com/icon/premium/png-512-thumb/git-branch-icon-svg-download-png-10369479.png" alt="" />
+          <img src="https://cdn.iconscout.com/icon/premium/png-512-thumb/git-branch-icon-svg-download-png-10369479.png" alt="illustrator of github icon" />
         </div>
         <h2>3. What is a branch in Git?</h2>
         <p>