Add draft warning.

themes/vanilla/assets/scss/style.scss

@@ -233,3 +233,10 @@ figure {
 .twitter-tweet {
     margin: auto;
 }
+
+.draft-warning {
+    @include bordered-block;
+    padding: 0.5rem;
+    background-color: #ffee99;
+    border-color: #f5c827;
+}

themes/vanilla/layouts/blog/single.html

@@ -18,6 +18,15 @@
         </div>
     </div>
     {{ end }}
+
+    {{ if .Draft }}
+    <div class="draft-warning">
+        <em>Warning!</em> This post is a draft. At best, it may contain grammar mistakes;
+        at worst, it can include significant errors and bugs. Please
+        use your best judgement!
+    </div>
+    {{ end }}
+
     {{ .Content }}
 </div>
 {{ end }}