Add XML sitemap.

robots.txt

@@ -1,2 +1,6 @@
 # www.robotstxt.org
-User-agent: *
+
+User-agent: *
+Disallow: /assets
+
+Sitemap: /sitemap.xml

sitemap.xml

@@ -0,0 +1,22 @@
+---
+layout: nil
+---
+<?xml version="1.0" encoding="utf-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+	<url>
+		<loc>{{ site.info.uri }}</loc>
+		<lastmod>{{ site.time | date: "%Y-%m-%d" }}</lastmod>
+		<changefreq>daily</changefreq>
+		<priority>1.0</priority>
+	</url>
+	{% for post in site.posts %}
+		<url>
+			<loc>{{ site.info.uri }}{{ post.url }}</loc>
+			{% if post.date %}
+				<lastmod>{{ post.date | date: "%Y-%m-%d" }}</lastmod>
+			{% else %}
+				<lastmod>{{ site.time | date: "%Y-%m-%d" }}</lastmod>
+			{% endif %}
+		</url>
+	{% endfor %}
+</urlset>