I think a link to the Readme.md might be more useful because it explains in detail what it is, why you might find it useful, and how to use it. The Readme.md contains a link to the sandbox fairly early on, but the sandbox doesn‘t seem to provide an easy way to get to the documentation (language info, API info, etc).
k doesn't have any valuable documentation to begin with, so language info wouldn't be much better than what you could get by doing a WWW search. The best way to learn is by doing, and the examples are really well commented.
My take: I don't think this is an issue. "What it is" is a sandbox for graphical K programs, which is already provided in the title. Given that K is already rather niche, and sandboxes are meant for playing with rather than general use programming, it seems like this toy isn't targeted towards a general audience and has no obligation to explain itself further than "K in your browser".
And apple is a horrible name for a computer because you may find fruit, amazon fire will give you trees in flames, and word, office, windows... It is difficult to find things when you do not know what you are searching for.
