Add timestamp to the template variables

Add index generation timestamp as a variable available to template
authors ("timestamp").

Change-Id: I7607f0c7eebaad1adca2d6e92a356a3dab1f015b

meetings/example.jinja

@@ -16,3 +16,5 @@ Chair (to contact for more information): {{ meeting.chair }}</p>
 {{ meeting.description|urlize }}
 
 {% endfor %}
+
+<p><i>Page generated on {{ timestamp }} UTC</i></p>

yaml2ical/index.py

@@ -10,6 +10,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import datetime
 import jinja2
 import logging
 import os
@@ -31,6 +32,7 @@ def convert_meetings_to_index(meetings, template, output_file):
     template = env.get_template(template_file)
 
     with open(output_file, "w") as out:
-        out.write(template.render(meetings=meetings))
+        out.write(template.render(meetings=meetings,
+                                  timestamp=datetime.datetime.utcnow()))
 
     logging.info('Wrote %d meetings to index.' % (len(meetings)))