Add test post to demo site

docs/_posts/2012-03-12-layout-external-hero-image.md

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+---
+title: "Layout: External Hero Image"
+image: 
+  path: https://source.unsplash.com/random/1024x600
+  thumbnail: https://source.unsplash.com/random/400x300
+categories:
+  - Layout
+tags:
+  - content
+  - image
+  - layout
+last_modified_at: 2017-03-17T10:46:49-04:00
+---
+
+This post should display a large hero image at the top of a page.
+
+This post tests a horizontal image using the following YAML Front Matter:
+
+```yaml
+image: https://source.unsplash.com/random/1024x600
+```
+
+Hero images can also be assigned like this:
+
+```yaml
+image:
+  path: https://source.unsplash.com/random/1024x600
+```