Update the issue template

Summary:
I notice most people filing issues are ignoring the issue template. I think we should try making it more concise, in particular asking people to provide a rnplay.org reproduction if it is possible.
Closes https://github.com/facebook/react-native/pull/10526

Differential Revision: D4070980

Pulled By: hramos

fbshipit-source-id: 0781fb9e410d50f8000b6c8cacfd5e5f9e881317