Placeholder Sky start page.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/677513002

examples/home.sky

+#!mojo mojo:sky
+<style>
+ h1 { font-size: 2em; margin: 1em; }
+ p { margin: 0.5em 1em; color: #bcd8f5; font-weight: 900; }
+</style>
+<h1>about:blank</h1>
+<p>Welcome to Sky!</p>