Fix install link by adding .html extension

Author: TorstenDittmann

apps/docs/index.html

@@ -8,7 +8,7 @@ <h4>
 				later—build it now.
 			</h4>
 			<div class="actions">
-				<a role="button" href="/install">Get started</a>
+				<a role="button" href="/install.html">Get started</a>
 				<a
 					href="https://github.com/TorstenDittmann/launch-css"
 					target="_blank"