Announce T-shirt campaign

[clalancette]

Humble: https://discourse.ros.org/t/humble-hawksbill-logo-and-tshirts/25395

Iron: https://discourse.ros.org/t/iron-irwini-logo-and-t-shirts/31214

Also, now that the logo is public: Note: Do not add svg for full res files to Github as we still want to protect copyright or redistribution rights.

• Add it to the artwork repository: https://github.com/ros-infrastructure/artwork
• Add the turtlesim icon: https://github.com/ros/ros_tutorials/pull/140
• Add the graphic to the documentation:https://github.com/ros2/ros2_documentation/pull/2495
• Add the graphic to the front page of https://docs.ros.org/ - basically, ssh into the host (rosbot@docs.ros.org), go to /var/www/docs.ros.org , cd .artwork , git pull , cd .. , edit index.html to point to artwork