OG Images for Twitter, FB, and Slack

[emilybrick]

(original PR for reference)

After doing a bit of research, I think we should create an OG image that works for all three platforms rather than try to style Facebook's preview differently.

As per the developer documentation, 1200 by 630 is the recommended size. You can, however, set separate images for Twitter and Facebook (as Atom is doing now, documented a bit here) but they're still the same size (both 1200 by 630).

Because we have a square OG image, It looks like even on Twitter our OG images are getting cropped:

which we could solve by fixing that aspect ratio to the recommended dimensions.

Though the square aspect ratio works for Slack, I think we can adjust the composition to work well in a 1200 x 630 frame. Let me know your thoughts and I can drop a few iterations in here at that size (for both primer.style & /components)

[emplums]

I agree this seems like the right way to go about it!

[ashygee]

Closing this issue and continuing conversation in #85.