Playground for react-flow

[arjungarg07]

Currently, we don't have any playground where one could do some changes and see the changes in the flow in real-time.

It would be really good if we could have playgrounds like: mermaid, plantUML, dotUML

Thoughts?

[RickeyWard]

I love this idea, but this is a bit of a complicated to use library and to have a worthwhile sandbox experience it would be better to include a link that spins up a new, current codesandbox and as it would just so happen @moklick already made templates on codesandbox for react-flow in both js and ts.

Here's a fresh one, knock yourself out.
https://codesandbox.io/s/react-flow-starter-ou8or