Add a better opengraph image

[agjohnson]

I'll update the current opengraph image with a temporary adjustment, but I'd like to redo this again in a more polished way. This was originally surfaced with:

• New vertical logo version #1 (comment)

The old image has a lot of unused whitespace, the current opengraph image uses a stacked version of our wordmark that isn't consistent with all of our other usage, and neither have any color to them.