Add alert mentioning that the project is not under development.

Author: XhmikosR

source/_includes/header.html

@@ -69,6 +69,15 @@ <h4><span class="fa fa-exclamation-circle" aria-hidden="true"></span> Warning</h
                 <p>You are using an <strong>outdated</strong> browser. Please <a class="alert-link" href="https://browsehappy.com/">upgrade your browser</a> to improve your experience.</p>
             </div>
         <![endif]-->
+        <div class="container">
+            <div class="row">
+                <div class="col-xs-12 col-md-8 center-block main-alert">
+                    <div class="alert alert-danger text-center" role="alert">
+                        MPC-HC is not <a class="alert-link" href="/2017/07/16/1.7.13-released-and-farewell/">under development since 2017</a>. Please switch to something else.
+                    </div>
+                </div>
+            </div>
+        </div>
         <nav class="navbar navbar-default navbar-fixed-top">
             <div class="container">
                 <div class="row">

source/assets/css/style.css

@@ -327,6 +327,11 @@ h6[id]::before {
     text-align: center;
 }
 
+.main-alert {
+    float: none;
+    margin-bottom: 30px;
+}
+
 
 .mpc-team .team-member a {
     color: #555;