Add GitHub organisation logo

[xeho91]

What?

Provide a logo asset for GitHub organisation.

Why?

Improve brand, credibility, encouragement to get involved.

How?

Update the organisation avatar, add it to the organisation profile README.md file, and give credit to the author & link to reach out (if agreed).

Requirements

• square version - to fit the avatar, preferably in the circle, so it doesn't get cropped.
• scalable vector format (SVG)
• Needs to include Rustacean community mascot - Ferris - https://www.rustacean.net/