Fix HTML validation errors in first article

Author: codebyra

Wireframe/index.html

@@ -14,7 +14,7 @@ <h1>Understanding Developer Tools</h1>
     <main>
       <article>
         <img src="placeholder.svg" alt="README file illustration" />
-        <h2>What is the purpose of a README file?</h2i>
+        <h2>What is the purpose of a README file?</h2>
         <p>A README explains what a project does, how to install it, and how to use it.</p>
         <a href="#">Learn more</a>
       </article>