Add a link to the league leaderboard to the homepage

[PeterJCLaw]

This shows that the virtual competition has happened and that teams have started earning points.

Sam & I also eyeballed:

• putting this new section on the right
• linking "Virtual Competition" (to the event page), and
• adding an <abbr> around "Virtual Competition" (with a title saying what it is)

but we think that this probably looks best.

Proposed:

with link:

with <abbr>:

right hand side: