add a demo feature (see #16)

budget/templates/home.html

@@ -7,7 +7,7 @@
 <div id="header">
     <div class="slide">
         <h1><span>Manage your shared <br>expenses easily</span></h1>
-        <a href="about.html" class="about_link">Try out the demo</a>
+        <a href="{{ url_for("demo") }}" class="about_link">Try out the demo</a>
     </div>
 </div>
 {% endblock %}

budget/web.py

@@ -123,6 +123,12 @@ def exit():
     session.clear()
     return redirect(url_for("home"))
 
+@app.route("/demo")
+def demo():
+    project = Project.query.get("demo")
+    session[project.id] = project.password
+    return redirect(url_for("list_bills", project_id=project.id))
+
 @app.route("/<project_id>/invite", methods=["GET", "POST"])
 def invite():