Add instance settings.

Addresses: #58

Currently implemented:

* Instance name
* Instance description
* Code of conduct
* Allow registration

I decided to store this in the database so that settings can be easily
changed at runtime through the web interface. (This web interface does
not exist.)

fedireads/templates/about.html

@@ -0,0 +1,21 @@
+{% extends 'layout.html' %}
+{% block content %}
+<div class="content-container">
+    <h2>About {{ site_settings.name }}</h2>
+    <p>
+    {{ site_settings.instance_description }}
+    </p>
+
+    <p>
+    <small>
+    <a href="/login/">Login or Create an Account</a>
+    </small>
+    </p>
+
+    <h2>Code of Conduct</h2>
+    <p>
+    {{ site_settings.code_of_conduct }}
+    </p>
+
+</div>
+{% endblock %}