fix: set links in demo html

so that it's clickable (they don't lead anywhere tho)

demo.html

···
     <header>
       <h1>dev.css Demo</h1>
       <nav>
-        <a>Home</a>
-        <a>About</a>
-        <a>Portfolio</a>
-        <a>Awesome</a>
-        <a>Sauce</a>
+        <a href="">Home</a>
+        <a href="">About</a>
+        <a href="">Portfolio</a>
+        <a href="">Awesome</a>
+        <a href="">Sauce</a>
       </nav>
     </header>