Add script to render upcoming events on index page

[FloorD]

I just spend a good half an hour updating the list of events on the events.html page and the index page (there were some old events listed as upcoming etc):

https://github.com/railsgirls/railsgirls/pull/555

... and it left me thinking that there should be an automated way for this. I despise manual labor and judging by the fact that no-one else bothered to update this earlier, I guess I am not the only one :wink:

[alicetragedy]

:+1: omg yes..

[Bertg]

Is this ticket included in #557 ? Maybe close this one in favour of the later?

[abelards]

I suggest we close #556 and start working on #557 -- for which I added the Jekyll tag. Anyone with an opinion is welcome :)

[khendrikse]

I made something for this in: https://github.com/railsgirls/railsgirls/pull/1640

Not perfect, but should work for now.