doc: Improve docs of zotonic_status site.

doc/tutorials/zotonic_status.rst

@@ -3,5 +3,35 @@
 The Zotonic "status" site
 =========================
 
-This manual should what the status site is, how to log in, and what options
-you have once logged in.
+The Zotonic "status" site is the first thing you see once you have
+installed Zotonic, when you do not have any sites configured yet. This
+is what it looks like:
+
+.. image:: /img/zotonic_status_login.png
+
+This site is also the `fallback` site for Zotonic.
+
+Since Zotonic supports virtual hosting, it uses the HTTP ``Host:``
+parameter to see which site should be served at which URL. If it does
+not find a ``Host:`` header, or if the host header does not correspond
+to any known Zotonic site, it shows the ``zotonic_status`` site
+instead.
+
+Logging in
+----------
+
+When logged in to the Zotonic status site, you can manage the running
+sites on the system: starting, stopping and upgrading them.
+
+Upon first visit, the site shows a friendly message, which tells
+visitors that the site they are looking at has probably not been
+configured correctly yes. It also asks for a password to log in.
+
+The password that is used for this is a generated password which sites
+in the ``priv/config`` file of the Zotonic folder.
+
+.. image:: /img/zotonic_status_sites.png
+
+The "update" buttons only appear when the site (or Zotonic itself) is
+under Mercurial or Git revision control. These buttons do a "pull"
+from the repository and then rebuild the system.