Add sitemap.xml and robots.txt files.

docs/robots.txt

@@ -0,0 +1,10 @@
+---
+layout: nil
+---
+
+# www.robotstxt.org/
+
+# Allow crawling of all content
+User-agent: *
+Disallow:
+Sitemap: {{ site.url }}/sitemap.xml

docs/sitemap.xml

@@ -0,0 +1,22 @@
+---
+layout: nil
+---
+<?xml version="1.0" encoding="UTF-8"?>
+<urlset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd" xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+  <url>
+    <loc>{{ site.url }}/</loc>
+    <lastmod>{{ site.time | date_to_xmlschema }}</lastmod>
+    <changefreq>daily</changefreq>
+    <priority>1.0</priority>
+  </url>
+  {% for page in site.html_pages %}
+  {% if page.layout != "home" %}
+  <url>
+    <loc>{{ site.url }}{{ page.url }}</loc>
+    <lastmod>{{ site.time | date_to_xmlschema }}</lastmod>
+    <changefreq>weekly</changefreq>
+    <priority>0.7</priority>
+  </url>
+  {% endif %}
+  {% endfor %}
+</urlset>