[WIP] Add "introduction picture" to the withastro org page on GitHub

[trueberryless]

This PR adds an image, which would be displayed right here (marked with green borders)

The image currently looks like this:

All the content visible within the borders would be moved downwards.

Before marking as ready:

• I'm planning to create some arrows with short text into different directions for orientation on the Organisation page of GitHub*
• Image is very large, so it takes some time to load, which is very annoying because then the pinned repos move down unexpected.
• Arrows don't match on mobile view (it looks good until width is less than 770px)

* What I mean with orientation arrows: I'm thinking of adding arrows into the direction of the people with a text like "look at those cool guys" and one into the direction of the repos (pinned) which says "check out some popular repos" and another that points above that says "Some general info"

Check out an example of such an image here: https://github.com/trueberryless-org

Please let me know what you think about such changes, if the are appreciated, give me feedback.
I think this would be a cool addition, but let's here the opinions of real maintainers!

[trueberryless]

If I may, I would really like to speak about this PR in the next Talking and Doc'ing and hear some opinions on this! 💬