Add 404 page template

layouts/404.html

@@ -0,0 +1,26 @@
+{{ define "main" }}
+    <section class="hero is-warning is-medium">
+        <div class="hero-body">
+            <div class="container">
+                <div class="columns">
+                    <main class="column is-8 is-offset-2">
+                        <p class="title">
+                            Page not found
+                        </p>
+                        <div class="content">
+                            <p>
+                                You could:
+                            </p>
+                            <ul>
+                                <li><a href="{{ "/" | relURL }}">Go back to the home page</a></li>
+                                <li><a href="{{ "/tags/" | relURL }}">Take a look at the list of tags</a></li>
+                                <li><a href="https://duckduckgo.com">Try searching for what you're looking for</a></li>
+                            </ul>
+                        </div>
+                    </main>
+                </div>
+            </div>
+        </div>
+
+    </section>
+{{ end }}

layouts/_default/baseof.html

@@ -5,7 +5,12 @@
 	<meta name="viewport" content="width=device-width, initial-scale=1">
 	<meta http-equiv="X-UA-Compatible" content="IE=edge">
 	<title>{{ .Title }}</title>
-	{{ with .Site.Params.description }}<meta name="description" content="{{ . }}">{{ end }}
+	{{ .Scratch.Set "desc" slice }}
+	{{ with .Site.Params.description }}{{ $.Scratch.Add "desc" (slice .) }}{{ end }}
+	{{ with .Site.Params.topics }}{{ $.Scratch.Add "desc" (slice (delimit . " & ")) }}{{ end }}
+	{{ if gt (len (.Scratch.Get "desc")) 0 }}
+	<meta name="description" content="{{ delimit (.Scratch.Get "desc") " " }}">
+	{{ end }}
 	{{ with .Site.Params.author }}<meta name="author" content="{{ . }}">{{ end }}
 	{{ $style := resources.Get "style/main.sass" | resources.ToCSS }}
 	<link rel="stylesheet" href="{{ $style.RelPermalink }}">