Update sponsorship section

[AmeliaBR]

[writing down the stuff I'd agreed to do but hadn't done, for better collaboration]

Our current status is that the workshop will be a W3C/OGC joint event (see #23), with NRCan and CAE as co-hosts.

That means we don't currently have any other sponsors to promote, so the current sidebar design will look rather empty.

Need to reword /redesign it to focus on attracting sponsors!

Gobe also suggested adding a proper heading on the call for participation page, “How can I sponsor the workshop?”. It would only need one-paragraph summary, then a link to the dedicated sponsorship page. But it means that it's part of the main text, and is included if we copy & paste the CFP into email blasts.

[AmeliaBR]

Closed as complete.