Primer.style homepage update: Release 2

[broccolini]

See #135

• Add new What's New section, highlighting the releases, follow the site design styles
• Automate this so that we don't have trouble keeping this up-to-date, see Adding action to auto-update releases data on deployment #108
• Consider updating News page to have "What's new" and "Releases" categories, see Proposal: News page reorganization  #121

[yaili]

Closing and adding as a reference for #135

[broccolini]

Reopening this as would like to schedule shipping this iteration soon. I've asked @edokoa to explore design updates but adding these sections can ship as is.

@colebemis - do you think you can take this on once you're freed up with Octicons?

[colebemis]

@broccolini Yep 👍