Add Creating Content docs section

Copying the Creating Content section from Picos content-sample/index.md. GitHubs markdown parser is not nearly as good as erusev/parsedown, so it was necessary to replace half of the contents with pure HTML...

_docs/creating_content.md

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+---
+toc:
+    creating-content:
+        _title: Creating Content
+        text-file-markup: Text File Markup
+        blogging: Blogging
+---
+
+## Creating Content
+
+Pico is a flat file CMS, this means there is no administration backend or
+database to deal with. You simply create `.md` files in the `content-sample`
+folder and that becomes a page. For example, this file is called `index.md`
+and is shown as the main landing page.
+
+If you create a folder within the content folder (e.g. `content-sample/sub`)
+and put an `index.md` inside it, you can access that folder at the URL
+`http://yoursite.com/?sub`. If you want another page within the sub folder,
+simply create a text file with the corresponding name and you will be able to
+access it (e.g. `content-sample/sub/page.md` is accessible from the URL
+`http://yoursite.com/?sub/page`). Below we've shown some examples of locations
+and their corresponing URLs:
+
+<table style="width: 100%; max-width: 40em;">
+    <thead>
+        <tr>
+            <th style="width: 50%;">Physical Location</th>
+            <th style="width: 50%;">URL</th>
+        </tr>
+    </thead>
+    <tbody>
+        <tr>
+            <td>content-sample/index.md</td>
+            <td><a href="%base_url%">/</a></td>
+        </tr>
+        <tr>
+            <td>content-sample/sub.md</td>
+            <td><del>?sub</del> (not accessible, see below)</td>
+        </tr>
+        <tr>
+            <td>content-sample/sub/index.md</td>
+            <td><a href="%base_url%?sub">?sub</a> (same as above)</td>
+        </tr>
+        <tr>
+            <td>content-sample/sub/page.md</td>
+            <td><a href="%base_url%?sub/page">?sub/page</a></td>
+        </tr>
+        <tr>
+            <td>content-sample/a/very/long/url.md</td>
+            <td><a href="%base_url%?a/very/long/url">?a/very/long/url</a> (doesn't exist)</td>
+        </tr>
+    </tbody>
+</table>
+
+If a file cannot be found, the file `content-sample/404.md` will be shown. You
+can add `404.md` files to any directory, so if you want to use a special error
+page for your blog, simply create `content-sample/blog/404.md`.
+
+### Text File Markup
+
+Text files are marked up using [Markdown][]. They can also contain regular HTML.
+
+At the top of text files you can place a block comment and specify certain
+attributes of the page. For example:
+
+<pre><code>---
+Title: Welcome
+Description: This description will go in the meta description tag
+Author: Joe Bloggs
+Date: 2013/01/01
+Robots: noindex,nofollow
+Template: index
+---</code></pre>
+
+These values will be contained in the `{% raw %}{{ meta }}{% endraw %}` variable
+in themes (see below).
+
+There are also certain variables that you can use in your text files:
+
+* <code>&#37;site_title&#37;</code> - The title of your Pico site
+* <code>&#37;base_url&#37;</code> - The URL to your Pico site; internal links
+  can be specified using <code>&#37;base_url&#37;?sub/page</code>
+* <code>&#37;theme_url&#37;</code> - The URL to the currently used theme
+* <code>&#37;meta.*&#37;</code> - Access any meta variable of the current page,
+  e.g. <code>&#37;meta.author&#37;</code> is replaced with `Joe Bloggs`
+
+### Blogging
+
+Pico is not blogging software - but makes it very easy for you to use it as a
+blog. You can find many plugins out there implementing typical blogging
+features like authentication, tagging, pagination and social plugins. See the
+below Plugins section for details.
+
+If you want to use Pico as a blogging software, you probably want to do
+something like the following:
+<ol>
+    <li>
+        Put all your blog articles in a separate <code>blog</code> folder in your <code>content</code>
+        directory. All these articles should have both a <code>Date</code> and <code>Template</code> meta
+        header, the latter with e.g. <code>blog-post</code> as value (see Step 2).
+    </li>
+    <li>
+        Create a new Twig template called <code>blog-post.twig</code> (this must match the
+        <code>Template</code> meta header from Step 1) in your theme directory. This template
+        probably isn't very different from your default <code>index.twig</code>, it specifies
+        how your article pages will look like.
+    </li>
+    <li>
+        Create a <code>blog.md</code> in your <code>content</code> folder and set its <code>Template</code> meta
+        header to e.g. <code>blog</code>. Also create a <code>blog.twig</code> in your theme directory.
+        This template will show a list of your articles, so you probably want to
+        do something like this:
+
+        {% raw %}<pre><code>{% for page in pages %}
+    {% if page.id starts with &quot;blog/&quot; %}
+        &lt;div class=&quot;post&quot;&gt;
+            &lt;h3&gt;&lt;a href=&quot;{{ page.url }}&quot;&gt;{{ page.title }}&lt;/a&gt;&lt;/h3&gt;
+            &lt;p class=&quot;date&quot;&gt;{{ page.date_formatted }}&lt;/p&gt;
+            &lt;p class=&quot;excerpt&quot;&gt;{{ page.description }}&lt;/p&gt;
+        &lt;/div&gt;
+    {% endif %}
+{% endfor %}</code></pre>{% endraw %}
+    </li>
+    <li>
+        Let Pico sort pages by date by setting <code>$config['pages_order_by'] = 'date';</code>
+        in your <code>config/config.php</code>. To use a descending order (newest articles
+        first), also add <code>$config['pages_order'] = 'desc';</code>. The former won't affect
+        pages without a <code>Date</code> meta header, but the latter does. To use ascending
+        order for your page navigation again, add Twigs <code>reverse</code> filter to the
+        navigation loop (<code>{&#37; for page in pages|reverse &#37;}...{&#37; endfor &#37;}}</code>)
+        in your themes <code>index.twig</code>.
+    </li>
+    <li>
+        Make sure to exclude the blog articles from your page navigation. You can
+        achieve this by adding <code>{&#37; if not page starts with "blog/" &#37;}...{&#37; endif &#37;}</code>
+        to the navigation loop.
+    </li>
+</ol>
+
+[Markdown]: http://daringfireball.net/projects/markdown/syntax