* Add Ko-fi icon
Add icon for Ko-fi, a service similar to Patreon, only without recurring
donations. Icon is based on the SVG found on their About page (https://ko-fi.com/home/about).
* Add Ko-fi details
Update the simple-icons.json file to include Ko-fi. The source links to
the page where the SVG was found, the color is taken from this SVG.
* Fix indentation for Ko-fi data
