Add an optional featured image (#252)

Bobby

27.46.2020 be94b5fd052b910d0b3704bea22d26214136f060

 exampleSite/content/posts/hugoisforlovers.md

@@ -12,6 +12,7 @@
    "golang",
]
series = ["Getting Started", "Hugo"]
featured_image = "https://imgs.xkcd.com/comics/angular_momentum.jpg"
+++

## Step 1. Install Hugo