Add Events link to Geode site footer

From mbretl:

ASF has created a new tool for scanning TLP sites for compliance and other
requests. The new tool is located at https://whimsy.apache.org/site, with our own Geode report at https://whimsy.apache.org/site/project/geode. The report looks good, with only one missing requirement of an Events page.

When I searched for 'event' on the source of the tool, I found http://www.apache.org/events/README.txt, with more event information.

However, looking at the code, it is searching for: 'apache.org/events/'. So
we can either create the link as text or use the image as a link.