Please provide showcase (and docs) for RingUI

[reubenfirmin]

Since RingUI is JetBrains' own library, please provide it special treatment:

a) Create a standalone showcase (which does not use React - bear in mind that people using kotlinjs may be trying to avoid as much of the js ecosystem as possible)
b) Include docs, either in the showcase or in a hosted page, so that consumers of the wrapper library can reference kotlin docs directly rather than wade through (and have to convert between) js and kotlin docs