Add R support guidance in document

[wdr123]

Context

Hi, I develop a react app and want to use thebe to create an R sandbox in the webpage, but I found the doc lacks such guidance. So I tried by myself but find even if I use the official R binder-url recommended by mybinder.org, the default laugange is still python. Don't know why.

Proposal

Add R laugane kernel call guidance in kernel configuration part

Tasks and updates

• Add R laugane kernel configuation in Configure Thebe Tab of the documentation website.

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[stevejpurves]

Thanks for opening the issue @wdr123 and yes the docs do need work

Do you have some more information or something that reproduces what you are doing? are you specifically trying to use thebe or thebe-react?