Fix unique images for each article

Author: eyob-tech

Wireframe/index.html

@@ -14,7 +14,7 @@ <h1>Understanding Web Development</h1>
 
   <main>
     <article>
-      <img src="placeholder.svg" alt="A README file displayed in a code editor" />
+      <img src="https://picsum.photos/seed/readme/400/200" alt="A README file displayed in a code editor" />
       <h2>What is the purpose of a README file?</h2>
       <p>When you open someone's project for the first time,
       the README is the first thing you read. It tells you
@@ -26,7 +26,7 @@ <h2>What is the purpose of a README file?</h2>
     </article>
 
     <article>
-      <img src="placeholder.svg" alt="A hand-drawn wireframe sketch of a webpage layout" />
+      <img src="https://picsum.photos/seed/wireframe/400/200" alt="A hand-drawn wireframe sketch of a webpage layout" />
       <h2>What is the purpose of a wireframe?</h2>
       <p>Before writing a single line of code, designers and
       developers draw a wireframe. It is a simple sketch that
@@ -38,7 +38,7 @@ <h2>What is the purpose of a wireframe?</h2>
     </article>
 
     <article>
-      <img src="placeholder.svg" alt="A diagram showing how Git branches split from the main branch" />
+      <img src="https://picsum.photos/seed/gitbranch/400/200" alt="A diagram showing Git branches" />
       <h2>What is a branch in Git?</h2>
       <p>A branch in Git is like a safe copy of your project
       where you can make changes freely. While you work on